Implement proper tail-call stack reuse for test262 PTC coverage

Context

The configured test262 runner now has zero metadata skips, but 35 proper-tail-call files are excluded before enumeration because zig-js does not implement proper-tail-call stack reuse. These are listed in docs/.data/test262-excluded.tsv with reason proper-tail-calls.

Current behavior

Focused PTC probes recurse to the test262 $MAX_ITERATIONS depth and currently end in stack exhaustion rather than constant-stack tail calls.

Done when

• The interpreter/VM implements strict-mode proper tail calls where required by ECMAScript.
• The focused PTC paths in test/language and Proxy revocable PTC coverage pass without stack growth failures.
• The 35 proper-tail-calls entries are removed from conformance/test262.zig exclusions and docs/.data/test262-excluded.tsv.
• zig build test262 stays green with the promoted cases included in the scored denominator.

Implemented and pushed in 1fa9e65.\n\nPTC exclusions are removed from the configured runner. The focused PTC probes now pass:\n- test/language/expressions tco: 0 fail, 16 pass\n- test/language/statements tco: 0 fail, 18 pass\n- test/language/expressions/call tco: 0 fail, 6 pass\n- test/built-ins/Proxy revocable PTC was also verified during the work.\n\nThe full regenerated docs data is green at VALID 48,486/48,486 and NEGATIVE 4,669/4,669. This promoted 35 proper-tail-call cases from excluded to scored-passing.