Fix set buffer overflow

[cs01]

Fix Set buffer overflow with dedup and dynamic reallocation

Both Set<number> and Set<string> had a fixed 4-element buffer with no capacity check or reallocation. Adding more than 4 elements wrote past the buffer — silent corruption on x86_64, immediate crash on ARM64. This was the root cause of the macOS CI failures when compiling JSON.parse<T>() (the generatedStructs Set accumulated 6+ entries).

Changes

• set.ts — generateSetAdd and generateStringSetAdd now do:
  • Duplicate check before insert (linear scan with fcmp oeq / strcmp)
  • Capacity check (size == capacity)
  • Dynamic reallocation when full (double capacity, GC_malloc, memcpy)
• New test fixtures — set-overflow.ts (10 numeric elements), string-set-overflow.ts (8 string elements), nested-interface-access.ts, string-concat-assign.ts
• CI — Added self-hosting tests to the Linux glibc job (was only on musl and macOS)

Test plan

• npm test — 288 pass, 0 fail
• npm run verify:quick — self-hosting passes