[MangelMaxime]

@dbrattli Here is what I found while reviewing #5062

Summary

Fixes async cleanup ordering and generic unit continuations in the Python runtime, with the same
fixes mirrored in the TypeScript runtime where they applied.

Runtime fixes (Python and TypeScript)

• TryFinally and Using install the cleanup continuation before the cancellation checkpoint, so a
  pre-cancelled token still runs compensation.
• TryFinally claims settlement under a lock in Python; on_cancel can arrive from another thread
  while on_success runs on the loop.
• Trampoline gains a completed flag (Python now matches TypeScript). After a terminal continuation
  runs, exceptions thrown by continuation code propagate instead of being routed back to on_error,
  which previously re-entered a succeeded try/with handler.
• protected_bind and TryWith only guard the binder or handler evaluation, not the resulting
  computation.
• from_continuations rejects a second completion with InvalidOperationException, matching .NET.
  from_continuations_unit is now built on top of it and shares the guard.
• MailboxProcessor.PostAndAsyncReply delivers exactly once when the reply races with the poster's
  start, and ignores a second Reply, matching .NET AsyncReplyChannel.
• Python Trampoline.run only looks up the event loop on the hijack path and runs inline when no loop
  is running.

Python compiler

• Callbacks whose generic parameter is instantiated to unit are wrapped with erase_unit_callable
  so Pyright accepts the erased unit argument. This now also covers spread (ParamArray) calls,
  curried applications, and calls to local generic functions.
• Local generic functions lose their declared signature at the call site (uncurryApplications
  emits empty signature types and the identifier type is already instantiated). The Python
  Context now records declared lambda types at Let/LetRec and uses them as a fallback.