fix: use a virtual executable name for Python workers (#444)

* fix: use a virtual executable name for Python workers

* test(python3): align isolation and cold-start timeout for finalization suite with existing tests

- Add python3.finalization.test.ts to vitest.config.ts's forks poolMatchGlobs
  so it runs process-isolated like other python worker suites (required
  because defense-in-depth patches globalThis, shared across threads).
- Give the first test a 60s timeout to accommodate the cold CPython/WASM
  load (~9MB WASM + 4.3MB stdlib zip), matching the convention used by
  every other python3 test file.