fix(ci): skip mimalloc FFI and disable isolation for Miri

[anakrish]

• Add cfg(not(miri)) guards to mimalloc module, global allocator, and allocator-memory-limits code paths so Miri falls back to the default system allocator instead of calling unsupported FFI functions.
• Set MIRIFLAGS="-Zmiri-disable-isolation" in the workflow so tests that perform file I/O can run under Miri.
• Skip units/parse tests under Miri due to Float-vs-BigInt Number representation mismatch with Miri's soft-float emulation.

[Copilot]

Pull request overview

This PR adjusts allocator/memory-limit integration and CI settings so the crate can run under Miri by avoiding unsupported mimalloc FFI paths, relaxing Miri isolation for file I/O, and skipping a small set of known-incompatible YAML tests.

Changes:

• Guard mimalloc + allocator-memory-limits code paths with not(miri) so Miri uses the default allocator and avoids unsupported FFI.
• Update Miri GitHub Actions workflow to run tests with MIRIFLAGS="-Zmiri-disable-isolation" for file I/O.
• Skip specific YAML interpreter tests under Miri due to soft-float Number representation mismatches.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
tests/memory_limits.rs	Disable allocator/memory-limit tests under Miri where mimalloc integration is unavailable.
src/value.rs	Avoid allocator-memory-limits revalidation path under Miri.
src/utils/limits/mod.rs	Disable memory-limits module + exports under Miri and provide no-op fallbacks.
src/tests/interpreter/mod.rs	Skip two known-failing YAML unit test files under Miri.
src/rvm/vm/machine.rs	Disable VM memory-limit checks/imports under Miri.
src/lib.rs	Hide allocator-memory-limits re-exports under Miri.
src/interpreter.rs	Disable interpreter memory-limit checks under Miri.
mimalloc/src/lib.rs	Prevent building/using mimalloc modules and global allocator under Miri.
.github/workflows/miri.yml	Configure Miri runs to disable isolation so file I/O tests can execute.

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[Copilot]

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated no new comments.

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