fix(build): adapt Go runtime sources for LLGo wasm32

[cpunion]

Summary

• patch Go runtime heap geometry for LLGo native wasm32 pointers, including the Go 1.26 arena-size change
• use the 32-bit hash fallback on pre-1.26 wasm builds
• replace selected Go wasm assembly in internal/bytealg, internal/chacha8rand, and internal/runtime/atomic with portable source patches
• suppress only the assembly files replaced by a target-specific source patch
• cover the assembly-skip, directory-skip, malformed build-constraint, and wasm runtime type-check paths

This is the foundational source-adaptation part of #2080 and must merge first. #2081 is stacked on this PR and contains the runtime host-dependency changes plus gated end-to-end wasm CI. This PR intentionally does not close #2080 by itself.

Validation

Rebased onto main@73fa30fbf; the single functional commit is patch-identical to the previous PR head.

• macOS arm64 / Go 1.26.5: full internal/build test suite passes
  • 73.5% statement coverage
• Linux amd64 / Go 1.26.5: full internal/build test suite passes
• macOS arm64 and Linux amd64:
  • the previous CI failure path now passes on current main
  • c-shared and c-archive build, C link, execution, and explicit DWARF lookup all pass

Go 1.24.2 and Go 1.26.5 end-to-end js/wasm and wasip1/wasm builds remain in the dependent #2081 validation and will be rerun only after this parent PR is green.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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