[PWGUD] modify mc producer & dihadron codes

[miedema-11]

1. an improved version for flow mc
2. add event selection switch for dihadron

[github-actions]

O2 linter results: ❌ 0 errors, ⚠️ 1 warnings, 🔕 2 disabled

[alibuild]

Error while checking build/O2Physics/code-check for c651528 at 2026-08-03 10:56:

## sw/BUILD/O2Physics-code-check-latest/log
--
========== List of issues found ==========
++ echo 'Found 12 errors and 30 warnings.'
Found 12 errors and 30 warnings.
++ [[ 12 -gt 0 ]]
++ cat /sw/BUILD/bd5807f22e16e1e8d64c862c32af69d51279cf70/O2Physics-code-check/errors.txt
PWGUD/Tasks/flowCorrelationsUpc.cxx:59:78: error: macro argument should be enclosed in parentheses [bugprone-macro-parentheses,-warnings-as-errors]
PWGUD/Tasks/flowCorrelationsUpc.cxx:61:8: error: constructor does not initialize these fields: ccdb [cppcoreguidelines-pro-type-member-init,-warnings-as-errors]
PWGUD/Tasks/flowCorrelationsUpc.cxx:125:48: error: redundant boolean literal supplied to boolean operator [readability-simplify-boolean-expr,-warnings-as-errors]
PWGUD/Tasks/flowCorrelationsUpc.cxx:329:29: error: the parameter 'track' is copied for each invocation but only used as a const reference; consider making it a const reference [performance-unnecessary-value-param,-warnings-as-errors]
PWGUD/Tasks/flowCorrelationsUpc.cxx:366:14: error: redundant boolean literal in conditional return statement [readability-simplify-boolean-expr,-warnings-as-errors]
PWGUD/Tasks/flowCorrelationsUpc.cxx:377:40: error: redundant boolean literal supplied to boolean operator [readability-simplify-boolean-expr,-warnings-as-errors]
PWGUD/Tasks/flowCorrelationsUpc.cxx:405:29: error: the parameter 'collision' is copied for each invocation but only used as a const reference; consider making it a const reference [performance-unnecessary-value-param,-warnings-as-errors]
PWGUD/Tasks/flowCorrelationsUpc.cxx:405:48: error: the parameter 'tracks' is copied for each invocation but only used as a const reference; consider making it a const reference [performance-unnecessary-value-param,-warnings-as-errors]
PWGUD/Tasks/flowCorrelationsUpc.cxx:430:33: error: the parameter 'tracks1' is copied for each invocation but only used as a const reference; consider making it a const reference [performance-unnecessary-value-param,-warnings-as-errors]
PWGUD/Tasks/flowCorrelationsUpc.cxx:430:50: error: the parameter 'tracks2' is copied for each invocation but only used as a const reference; consider making it a const reference [performance-unnecessary-value-param,-warnings-as-errors]
PWGUD/Tasks/flowCorrelationsUpc.cxx:446:24: error: narrowing conversion from 'Double_t' (aka 'double') to 'int' [bugprone-narrowing-conversions,-warnings-as-errors]
PWGUD/Tasks/flowCorrelationsUpc.cxx:500:13: error: Variable 'rad' with floating point type 'double' should not be used as a loop counter [clang-analyzer-security.FloatLoopCounter,-warnings-as-errors]
++ [[ 30 -gt 0 ]]
++ cat /sw/BUILD/bd5807f22e16e1e8d64c862c32af69d51279cf70/O2Physics-code-check/warnings.txt
PWGUD/Tasks/flowCorrelationsUpc.cxx:215:40: warning: statement should be inside braces [readability-braces-around-statements]
PWGUD/Tasks/flowCorrelationsUpc.cxx:247:37: warning: statement should be inside braces [readability-braces-around-statements]
PWGUD/Tasks/flowCorrelationsUpc.cxx:249:37: warning: statement should be inside braces [readability-braces-around-statements]
PWGUD/Tasks/flowCorrelationsUpc.cxx:251:29: warning: statement should be inside braces [readability-braces-around-statements]
PWGUD/Tasks/flowCorrelationsUpc.cxx:253:29: warning: statement should be inside braces [readability-braces-around-statements]
PWGUD/Tasks/flowCorrelationsUpc.cxx:317:37: warning: statement should be inside braces [readability-braces-around-statements]
PWGUD/Tasks/flowCorrelationsUpc.cxx:398:18: warning: statement should be inside braces [readability-braces-around-statements]
PWGUD/Tasks/flowCorrelationsUpc.cxx:411:34: warning: statement should be inside braces [readability-braces-around-statements]
PWGUD/Tasks/flowCorrelationsUpc.cxx:418:57: warning: statement should be inside braces [readability-braces-around-statements]
PWGUD/Tasks/flowCorrelationsUpc.cxx:450:34: warning: statement should be inside braces [readability-braces-around-statements]
PWGUD/Tasks/flowCorrelationsUpc.cxx:465:36: warning: statement should be inside braces [readability-braces-around-statements]
PWGUD/Tasks/flowCorrelationsUpc.cxx:468:58: warning: statement should be inside braces [readability-braces-around-statements]
PWGUD/Tasks/flowCorrelationsUpc.cxx:470:72: warning: statement should be inside braces [readability-braces-around-statements]
PWGUD/Tasks/flowCorrelationsUpc.cxx:472:83: warning: statement should be inside braces [readability-braces-around-statements]
PWGUD/Tasks/flowCorrelationsUpc.cxx:507:26: warning: statement should be inside braces [readability-braces-around-statements]
PWGUD/Tasks/flowCorrelationsUpc.cxx:534:35: warning: statement should be inside braces [readability-braces-around-statements]
PWGUD/Tasks/flowCorrelationsUpc.cxx:546:33: warning: statement should be inside braces [readability-braces-around-statements]
PWGUD/Tasks/flowCorrelationsUpc.cxx:600:68: warning: statement should be inside braces [readability-braces-around-statements]
PWGUD/Tasks/flowCorrelationsUpc.cxx:612:35: warning: statement should be inside braces [readability-braces-around-statements]
PWGUD/Tasks/flowMcUpc.cxx:867:81: warning: statement should be inside braces [readability-braces-around-statements]
PWGUD/Tasks/flowMcUpc.cxx:874:24: warning: statement should be inside braces [readability-braces-around-statements]
PWGUD/Tasks/flowMcUpc.cxx:876:27: warning: statement should be inside braces [readability-braces-around-statements]
PWGUD/Tasks/flowMcUpc.cxx:878:27: warning: statement should be inside braces [readability-braces-around-statements]
PWGUD/Tasks/flowMcUpc.cxx:880:29: warning: statement should be inside braces [readability-braces-around-statements]
PWGUD/Tasks/flowMcUpc.cxx:900:35: warning: statement should be inside braces [readability-braces-around-statements]
PWGUD/Tasks/flowMcUpc.cxx:903:27: warning: statement should be inside braces [readability-braces-around-statements]
PWGUD/Tasks/flowMcUpc.cxx:907:33: warning: statement should be inside braces [readability-braces-around-statements]
PWGUD/Tasks/flowMcUpc.cxx:916:166: warning: statement should be inside braces [readability-braces-around-statements]
[0 more errors; see full log]

Full log here.