infer: exclude aliasCache scratch bits from TypeDecl hash

[borisbat]

Summary

PR #2849 added aliasCacheValid / aliasCacheHasAlias bits to the TypeDecl::flags union for the lazy findAlias subtree cache. They are runtime scratch state — set on the first findAlias call, retained for later calls — not part of the type's semantic identity. They were leaking into getLookupHash, getSemanticHash, and getOwnSemanticHash via hashmix(hash, flags) / hb.update(flags).

Within a single compile this is deterministic (same input ⇒ same cache lifecycle ⇒ same bit state). Across two semantically equivalent TypeDecls whose findAlias-call lifecycles differ (one cached, one not), the hashes diverge — risky for type interning and AOT semantic hashing across module boundaries.

This adds flagsWithoutAliasCache(td) — save the two bits via const_cast, clear them, read flags, restore — and uses it at the 3 hash sites instead of raw flags.

No ABI change (bits stay in the flags union; the helper only touches them transiently during hash compute).

Test plan

• daslang.exe dastest/dastest.das -- --test tests/ — 9341 passed, 0 failed
• daslang.exe -jit tests/jit_tests/array.das + tests/decs/test_bulk_create.das — no verifier errors
• test_aot.exe -use-aot dastest/dastest.das -- --use-aot --test tests — 8685 passed, 0 failed
• No .das files changed (lint/format/detect-dupe not applicable)

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR prevents TypeDecl hash values from including lazy findAlias cache state, keeping lookup and semantic hashes tied to type identity rather than runtime scratch bits.

Changes:

• Adds flagsWithoutAliasCache to temporarily exclude aliasCacheValid and aliasCacheHasAlias.
• Uses the filtered flags in lookup, semantic, and own semantic hash generation.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.