Avoid boolean tests of debugger `trio.Event` handles

On `trio` 0.34, boolean tests of `trio.Event` raise. Debugger
setup/release, TTY-lock diagnostics and the RPC cancellation path
used truthiness to check whether optional event handles existed,
raising `NotImplementedError` instead of entering or leaving the
REPL and waiting for its release.

Use explicit `is None`/`is not None` checks for those five sites.
Keep `.is_set()` for the actual release-state decision and retain
the existing waits: an allocated pending event is not an absent
handle, nor does its existence mean it has been signaled.

Keep the debug-request comment beside its lock-release check.

(this patch was generated in some part by `opencode` using
`gpt-6.1-sol` (`openai`))

tractor/devx/debug/_trace.py

@@ -285,7 +285,7 @@ async def _pause(
     # the `PdbREPL`.
     repl_task: Thread|Task|None = DebugStatus.repl_task
     if (
-        not DebugStatus.repl_release
+        DebugStatus.repl_release is None
         or
         DebugStatus.repl_release.is_set()
     ):
@@ -849,7 +849,7 @@ async def _pause_from_bg_root_thread(
     stats: trio.LockStatistics= lock.statistics()
     assert stats.owner is task
     assert Lock._owned_by_root
-    assert DebugStatus.repl_release
+    assert DebugStatus.repl_release is not None
 
     # TODO: do we actually need this?
     # originally i was trying to solve wy this was

tractor/devx/debug/_tty_lock.py

@@ -172,7 +172,7 @@ class Lock:
             f'|_ .ctx_in_debug: {cls.ctx_in_debug}\n'
             f'|_ .req_handler_finished: {req}\n'
         )
-        if req:
+        if req is not None:
             req_stats: trio.EventStatistics = req.statistics()
             fields += f'  {req_stats}\n'
 
@@ -288,7 +288,8 @@ class Lock:
                 )
 
             elif (
-                req_handler_finished  # new IPC ctx debug request active
+                # new IPC ctx debug request active
+                req_handler_finished is not None
                 and
                 lock.locked()  # someone has the lock
             ):

tractor/runtime/_rpc.py

@@ -1137,7 +1137,7 @@ async def process_messages(
                         # runtime cancellation if this actor is
                         # currently in debug mode!
                         pdb_complete: trio.Event|None = debug.DebugStatus.repl_release
-                        if pdb_complete:
+                        if pdb_complete is not None:
                             await pdb_complete.wait()
 
                         # Either of  `Actor.cancel()`/`.cancel_soon()`