fix: reuse sources registered during URL resolution

[Siddharth (sidsri14)]

Summary

• recheck the original-URL source registry after asynchronous URL resolution
• reuse a concurrently registered source only when its content hash matches
• add a deterministic regression test for the two-context race

Closes #2342

Verification

• npm run test:unit -- --grep SourceContainer (1 passing)
• npm run test:types
• npm run compile
• dprint check src/adapter/sourceContainer.ts src/adapter/sourceContainer.test.ts
• eslint --max-warnings=0 src/adapter/sourceContainer.ts src/adapter/sourceContainer.test.ts
• git diff --check

The full unit run completed with 259 passing tests and 8 failures, all in the unchanged NodeBinaryProvider Windows PATH fixtures, where the host Node executable is selected instead of the checked-in fixture. Full lint likewise reaches an existing dprint violation in unchanged src/targets/node/nodeLauncher.ts:318; the changed files pass both dprint and ESLint directly.

[Siddharth (sidsri14)]

@microsoft-github-policy-service agree