Port Bun mock.module dynamic, spy, and live-binding matrix

Scope

Port the byte-identical js/bun/test/mock/mock-module.test.ts corpus and its three TypeScript fixtures. The file contains nine active tests plus one upstream todo.

This is the broader follow-on to #122 and #124, covering:

• async mock factories
• mock.restore and spyOn namespace restoration
• nonexistent package and relative module mocks
• file URL mock resolution
• require/import/require.resolve agreement
• repeated local module replacement with live imported bindings and re-exports
• repeated package replacement through an existing dynamic namespace
• builtin aliasing between fs/promises and node:fs/promises

Baseline

Home currently rewrites the whole file to one native todo:

• 0 pass
• 0 fail
• 0 unsupported
• 1 native todo

Acceptance

• Keep the corpus file and fixtures byte-identical to Bun.
• Run all nine active upstream tests as real tests.
• Preserve the single upstream todo without introducing Home-native todos.
• Implement stable live namespaces, lazy async factory handling, module overlay semantics, spy restoration, canonical builtin mock keys, and consistent require/import mock lookup.
• Add a permanent unchanged-corpus regression.
• Pass the exact file and full home_test gate.
• Commit and push as Chris Breuer with no coauthors.
• Link completion to #66.

Implemented and pushed in b15c3f7.

The byte-identical mock-module.test.ts corpus and all three fixtures now run through the Home bridge. The implementation adds:

• canonical mock keys for fs/promises and node:fs/promises
• lazy async factory normalization and caching
• descriptor-preserving mock overlays on original namespaces
• stable live dynamic namespaces across repeated replacements
• shared mock lookup for import, dynamic import, require, and require.resolve
• relative file URL normalization
• mock.restore spy restoration
• live local imports, re-export aliases, and originating re-export cell propagation

Validation:

• exact mock-module.test.ts: 9 pass, 0 fail, 0 unsupported, 1 upstream todo
• prior mock/6874: A 1/1 and B 1/1
• prior mock/6879: 2/2
• permanent unchanged-corpus regression asserts the 9-pass/1-upstream-todo shape
• all four corpus files are byte-identical to Bun
• formatting and diff checks pass
• full home_test gate passes with no failures

The commit is authored and committed as Chris Breuer with no coauthors. This follows #122 and #124 and advances #66.