Language: silence value-consuming @ CV fetch (#31881)

[PurHur]

Summary

• php-cfg represented @$cv as a dummy UnaryPlus fetch under silence but still returned the original CV, so echo / arithmetic / call-arg re-fetched after END_SILENCE and emitted Undefined variable.
• Materialize @$cv into an Assign temp under silence and forward that temp (null, not +null → 0). isErrorSuppressInnerExpr() now also treats unary/binary inner exprs so the suppress result slot is inherited.
• php-src: Zend/zend_compile.c ZEND_BEGIN_SILENCE / ZEND_END_SILENCE; Zend/zend_execute.c undefined-variable E_WARNING on CV fetch. PHP implementation: patches/php-cfg-error-suppress-cv-temp.patch + lib/Compiler.php. No new runtime/*.c.

Closes #31881

Test plan

• Issue repro VM vs Zend
• Issue repro JIT
• ./script/phpunit.sh --filter ErrorControlOperatorTest

Verification

./script/docker-exec.sh -- bash -lc 'php test/repro/maintainer_gap_at_silence_undef.php; echo "---ZEND---"; php bin/vm.php test/repro/maintainer_gap_at_silence_undef.php'

Zend and VM both: assign NULL, echo NULL, plus 1, callarg 0 + strlen(null) Deprecated, bare/print silent. No Undefined variable.

./script/docker-exec.sh -- bash -lc 'php bin/jit.php test/repro/maintainer_gap_at_silence_undef.php'

JIT: same stdout; stderr has only the strlen(null) Deprecated (plus an unrelated php-cfg implicit-nullable Deprecated). No Undefined variable.

./script/phpunit.sh --filter ErrorControlOperatorTest

OK (5 tests, 9 assertions) including at_silence_value_undef.phpt.

Not run: script/differential-sweep.sh, full ci-local.sh, north-star5-verify --strict.

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