fix(spec): read float JSON values like iceberg-java

[spicysharkco]

Which issue does this PR close?

• Part of JSON data-file helpers reject valid floats and silently corrupt non-finite partition values #3409.

What changes are included in this PR?

RawLiteral::try_into for PrimitiveType::Float rejected a double when (f64::from(v as f32) - v).abs() > f32::EPSILON. That is an absolute bound, so valid floats such as 100.1 and 123.456 failed with Unable to convert raw literal (double) fail convert to type float for: type mismatch. This path reads float partition values in deserialize_data_file_from_json and float Datum values.

The check is replaced by a plain v as f32. That is what iceberg-java does: SingleValueParser.fromJson checks isFloatingPointNumber() for FLOAT and returns floatValue() (SingleValueParser.java L73-L79). It is also what Literal::try_from_json already does for field defaults. A double with no exact f32 now narrows to the nearest one: 16777217.0 gives 16777216.0, where main returned an error.

Doubles outside the f32 range (for example 1e39, which becomes infinity) behave as on main and as floatValue(). That is the subject of #3333 and is not touched here.

Notes for reviewers:

• fix(spec): reject float overflow in raw literals #3333 edits the line this PR removes and relies on the check to reject overflow. Its test_raw_double_to_float_precision_loss also expects an error for 123.456789 and 123456789.0, which this PR accepts. If this lands first, fix(spec): reject float overflow in raw literals #3333 would need its own overflow check and that test would change.
• The non-finite half of JSON data-file helpers reject valid floats and silently corrupt non-finite partition values #3409 (NaN and +/-Infinity written as JSON null) is left open. Returning an error from Literal::try_into_json would make From<NestedField> for SerdeNestedField panic at datatypes.rs:649-650 (.expect on try_into_json) for a field whose default is NaN or infinite. Java's SingleValueParser.toJson writes quoted "NaN" and "Infinity" strings by default (Jackson QUOTE_NON_NUMERIC_NUMBERS), which its own fromJson cannot read back. Which behaviour do you want here?

Are these changes tested?

Unit tests in crates/iceberg/src/spec/values/tests.rs, which fail on current main and pass with this change:

• raw_literal_json_number_to_float: 100.1, 123.456, -123.456, f32::MAX, f32::MIN and the smallest subnormal, parsed with serde_json::from_str::<RawLiteral>, convert to exactly that f32.
• raw_literal_avro_double_to_float: the same values through Value::Double, both as the widened f32 and as the shortest decimal parsed to f64.
• raw_literal_double_without_exact_float_narrows_to_nearest: 16777217.0 becomes 16777216.0, and 1.0000000001 becomes 1.0.