[codex] support BigInt typed-array Atomics

[andrewtdiz]

Summary

Part of #2876.

This adds BigInt typed-array support to the deterministic Atomics operations that already route through the runtime: load, store, add, sub, and, or, xor, exchange, and compareExchange.

• accepts BigInt64Array and BigUint64Array views in the Atomics receiver validator
• reads/writes raw 64-bit lanes so signed and unsigned BigInt views preserve Node-style wrapping and return types
• applies Atomics ToBigInt operand behavior, including rejecting Number operands while still accepting booleans and strings
• keeps numeric integer typed-array behavior on the existing numeric path
• adds a Node parity fixture for signed/unsigned wrap, bitwise operations, compareExchange, and BigInt/Number coercion errors

Non-goals

• blocking Atomics.wait / waitAsync / notify behavior for BigInt views
• true inter-thread atomicity beyond Perry's current deterministic single-thread runtime behavior
• broader SharedArrayBuffer memory-model validation outside this Atomics operation slice
• unrelated numeric typed-array return-value nuances

Validation

• CARGO_TARGET_DIR=/tmp/perry-atomics-bigint-check cargo check -p perry-runtime -p perry-codegen -p perry-hir
• cargo fmt --all -- --check
• CARGO_TARGET_DIR=/tmp/perry-atomics-bigint-build cargo build --release --quiet -p perry -p perry-runtime -p perry-stdlib
• npm exec --yes --package=node@26 -- node --experimental-strip-types test-parity/node-suite/globals/atomics-bigint.ts
• PERRY_NO_AUTO_OPTIMIZE=1 /tmp/perry-atomics-bigint-build/release/perry test-parity/node-suite/globals/atomics-bigint.ts -o /tmp/perry_atomics_bigint && /tmp/perry_atomics_bigint
• PERRY_NO_AUTO_OPTIMIZE=1 CARGO_TARGET_DIR=/tmp/perry-atomics-bigint-build npm exec --yes --package=node@26 -- bash -lc './run_parity_tests.sh --suite node-suite --module globals --filter atomics'
• git diff --check
• ./scripts/check_file_size.sh