fix: ensure Worker subclasses are wrapped only once

[ryanking13]

fixes #125

Our _wrap_subclass had an issue that when there is a subclass that inherits the wrapped WorkerEntrypoint/DurableObject, the _wrap_subclass is called multiple times, double wrapping the env or ctx attributes.

We always had that issue but it was surfaced by my recent change in the DO (#112)

This fixes it by adding a guarder variable and applying the wrapper function only once.

[ask-bonk]

The test structure matches the existing patterns. The fix is clean, the approach is correct, and the tests are thorough. The implementation correctly handles all the edge cases:

1. Leaf class with no __init__ (inherits wrapped init)
2. Leaf class with its own __init__ (calls super)
3. Both DurableObject and WorkerEntrypoint hierarchies are tested
4. The test asserts that env is wrapped exactly once (not zero, not double)

LGTM

github run

[dom96]

Thanks! See comment for small refactoring nit.