[ViralBShah]

Stacked on #158. It will be rebased onto v11 once #158 merges.

#158 turns the GraphBLAS JIT off at init, because the jll's default compiler is the build machine's gcc path. This PR adds an opt-in way to turn it back on:

SuiteSparseGraphBLAS.jit!()                      # uses Sys.which("cc"), default cache ~/.SuiteSparse/GrB<ver>
SuiteSparseGraphBLAS.jit!(; compiler = "/usr/bin/gcc", cache = "/tmp/grbjit")
SuiteSparseGraphBLAS.jit!(false)

With the JIT on, GraphBLAS compiles kernels it doesn't ship precompiled and caches them for later sessions. Locally with system gcc, the first A[:, j] took 0.31 s to compile its kernel; the next call took 0.1 ms.

• The default flags assume gcc with OpenMP, so this works out of the box on Linux. macOS (Apple clang has no OpenMP) and Windows would need different flags; that's left for later.
• GxB_JIT_ERROR and GxB_OUTPUT_IS_READONLY now raise readable errors instead of "Unknown GraphBLAS Exception".
• The test (Linux with cc only) uses a temporary cache and checks that a kernel .so is compiled. It is added to test/libutils.jl.
• jit! is listed in the Utilities docs.

Pkg.test() passes locally on Julia nightly.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 65.65%. Comparing base (cde8c7f) to head (b5e6ef1).
⚠️ Report is 1 commits behind head on v11.

Additional details and impacted files

@@            Coverage Diff             @@
##              v11     #159      +/-   ##
==========================================
+ Coverage   65.59%   65.65%   +0.06%     
==========================================
  Files          54       54              
  Lines        4441     4449       +8     
==========================================
+ Hits         2913     2921       +8     
  Misses       1528     1528              

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