fix(class): route Rust prop access through the declared slot and the getter/setter

[ptondereau]

Description

A Rust property value now goes into the declared property slot, so Exception::getMessage and other C callers do not leak it. Compound operators, unset, == and the engine property cache now use the Rust getter and setter.

Fixes #738

Checklist

• I have read the contribution guidelines and the code of conduct.
• I have added tests that prove my code works as expected.
• I have added documentation if applicable.
• I have added a migration guide if applicable.

[coveralls]

Coverage Report for CI Build 37217587832

Coverage decreased (-0.8%) to 70.157%

Details

• Coverage decreased (-0.8%) from the base build.
• Patch coverage: 210 uncovered changes across 1 file (0 of 210 lines covered, 0.0%).
• 8 coverage regressions across 2 files.

Uncovered Changes

File	Changed	Covered	%
src/zend/handlers.rs	210	0	0.0%

Coverage Regressions

8 previously-covered lines in 2 files lost coverage.

File	Lines Losing Coverage	Coverage
src/zend/handlers.rs	7	0.0%
crates/introspection/src/stub.rs	1	88.46%

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Coverage Stats

Relevant Lines:	14563
Covered Lines:	10217
Line Coverage:	70.16%
Coverage Strength:	60.64 hits per line

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💛 - Coveralls

[codspeed]

Merging this PR will not alter performance

✅ 30 untouched benchmarks
🆕 6 new benchmarks

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
🆕	property_compares[1]	N/A	125.2 ms	N/A
🆕	property_compares[10]	N/A	125.2 ms	N/A
🆕	property_compares[100000]	N/A	544.3 ms	N/A
🆕	property_compound_ops[1]	N/A	125.2 ms	N/A
🆕	property_compound_ops[10]	N/A	125.2 ms	N/A
🆕	property_compound_ops[100000]	N/A	698.5 ms	N/A

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_{Comparing fix/prop-getter-slot-leak (70855cb) with master (844d387)}