Triage fixes: __le-across-yield (#97), break wording (#95), closure caching (#96), 5.5 vararg aliasing (#94)

[ianm199]

Triage pass over the freshly-opened issues: verified each against the current code + reference binaries for all 5 versions, then fixed the four well-scoped ones. Each fix verified vs the matching /tmp/lua-refs reference (5.1.5/5.2.4/5.3.6/5.4.7/5.5.0), the official tests, GC canaries, the 112-test multiversion oracle, and the full 5.4 parity sweep (36/44 — the 8 DIVERGE are the known PRNG/limit/locale/codegen set, unchanged).

Fixes

#97 — __le from __lt across a yield (5.1–5.4) fix(vm)
Re-introduced the CIST_LEQ mark (bit 13, as C). The synchronous derive in call_order_tm was already correct; the gap was finish_op not negating on resume after the __lt yielded. Was a silent wrong answer (inverted comparison). 5.5 correctly still raises (derivation removed).

#95 — break outside loop wording per version fix(parser)
Version-gated: 5.1 eager no loop to break, 5.2/5.3 deferred <break> at line N not inside a loop, 5.4 break outside loop at line N, 5.5 eager break outside loop near 'break'. Message text now matches reference on all 5. (Filed #105 for the separate, pervasive 5.1 special-token quoting gap — different root cause in the shared lexer.)

#96 — loop-built-closure == caching (5.2/5.3) fix(vm)
Added Proto.cache (C's getcached): OP_CLOSURE reuses the last closure built from a proto when upvalues are identical. Gated to 5.2/5.3 (issue said 5.3-only, but reference shows 5.2 caches too); inert on 5.4 (cache stays None).

#94 — 5.5 named-vararg ...t shared storage fix(vm)
... now unpacks live from the packed table t (count = its n field), so mutating t shows through a later ... (99 2 3, not 1 2 3). Adds Proto.vararg_table_reg, reconstructed during undump by scanning for OP_VARARGPACK so string.dump round-trips without diverging from C's bytecode layout. vararg.lua now passes on 5.5 (was the sole L111 failure).

Not in scope (architectural — documented, not driven-by)

• debug: version-gate line-hook fidelity (back-edge rule + TEST/JMP line attribution) #92 line-hook fidelity — two-crate version-gated change with cross-version line-number regression risk.
• gc: implement generational collector + per-version default mode #93 / Phase D: real GC byte accounting — remove the gc.lua observable simulations #104 generational GC — needs real byte accounting first; the triage found gc.lua's MATCH currently rests on simulated memory observables (api.rs:2004/2073). Filed Phase D: real GC byte accounting — remove the gc.lua observable simulations #104 as the prerequisite.
• Support Lua 5.5 (track upstream work release) #20 5.5 tracker epic.

Closes #97, #95, #96, #94.