Avoid silent `stackscope`-test fail due to dep

Oddly my env was borked bc a missing sub-dep (`typing-extensions`
apparently not added by `uv` for `stackscope`?) and then `stackscope`
was silently failing import and caused the shield-pause test to also
fail (since it couldn't match the expected `log.devx()` on console). The
import failure is not very explanatory due to the `log.warning()`;
change it to `.error()` level.

Also, explicitly import `_sync_pause_from_builtin` in
`examples/debugging/restore_builtin_breakpoint.py` to ensure the ref is
exported properly from `.devx.debug` (which it wasn't during dev of the
prior commit Bp).

examples/debugging/restore_builtin_breakpoint.py

@@ -4,6 +4,11 @@ import sys
 import trio
 import tractor
 
+# ensure mod-path is correct!
+from tractor.devx.debug import (
+    _sync_pause_from_builtin as _sync_pause_from_builtin,
+)
+
 
 async def main() -> None:
 
@@ -13,6 +18,7 @@ async def main() -> None:
 
     async with tractor.open_nursery(
         debug_mode=True,
+        loglevel='devx',
     ) as an:
         assert an
         assert (

pyproject.toml

@@ -63,7 +63,6 @@ dev = [
   "stackscope>=0.2.2,<0.3",
   # ^ requires this?
   "typing-extensions>=4.14.1",
-
   "pyperclip>=1.9.0",
   "prompt-toolkit>=3.0.50",
   "xonsh>=0.19.2",

tractor/devx/_stackscope.py

@@ -237,7 +237,7 @@ def enable_stack_on_sig(
     try:
         import stackscope
     except ImportError:
-        log.warning(
+        log.error(
             '`stackscope` not installed for use in debug mode!'
         )
         return None
@@ -255,8 +255,8 @@ def enable_stack_on_sig(
         dump_tree_on_sig,
     )
     log.devx(
-        'Enabling trace-trees on `SIGUSR1` '
+        f'Enabling trace-trees on `SIGUSR1` '
-        'since `stackscope` is installed @ \n'
+        f'since `stackscope` is installed @ \n'
         f'{stackscope!r}\n\n'
         f'With `SIGUSR1` handler\n'
         f'|_{dump_tree_on_sig}\n'