Support process and signal on wasm

[peter-jerry-ye]

Why

The wasm backend needs the async process APIs and global signal handling to behave like the native event loop. Without these imports, process cancellation and the signal package cannot run under moonrun.

Correctness

This adds wasm bindings for process and signal operations, keeps Windows-only signal paths as link-time stubs where the native package cannot deliver those signals programmatically, and routes Unix signal handling through the existing thread-pool completion path.

Scope

The change is limited to wasm process/signal bindings and enables the existing signal tests for wasm.

[coveralls]

Coverage Report for CI Build 781

Coverage decreased (-1.3%) to 75.9%

Details

• Coverage decreased (-1.3%) from the base build.
• Patch coverage: 82 uncovered changes across 3 files (0 of 82 lines covered, 0.0%).
• 3 coverage regressions across 2 files.

Uncovered Changes

File	Changed	Covered	%
src/process/process.mbt	43	0	0.0%
src/internal/event_loop/signal.mbt	20	0	0.0%
src/internal/event_loop/process.mbt	19	0	0.0%

Coverage Regressions

3 previously-covered lines in 2 files lost coverage.

File	Lines Losing Coverage	Coverage
src/internal/event_loop/network.mbt	2	75.0%
src/internal/event_loop/signal.mbt	1	41.18%

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Coverage Stats

Relevant Lines:	4776
Covered Lines:	3625
Line Coverage:	75.9%
Coverage Strength:	11652.91 hits per line

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💛 - Coveralls