Add timeouts around some context test bodies

Since with my in-index runtime-port to our native msg-spec it seems
these ones are hanging B(

- `test_one_end_stream_not_opened()`
- `test_maybe_allow_overruns_stream()`

Tossing in some `trio.fail_after()`s seems to at least gnab them as
failures B)

tests/test_context_stream_semantics.py

@@ -6,6 +6,7 @@ sync-opening a ``tractor.Context`` beforehand.
 
 '''
 from itertools import count
+import math
 import platform
 from pprint import pformat
 from typing import (
@@ -872,7 +873,7 @@ def test_one_end_stream_not_opened(
                 enable_modules=[__name__],
             )
 
-            with trio.fail_after(1):
+            with trio.fail_after(0.8):
                 async with portal.open_context(
                     entrypoint,
                 ) as (ctx, sent):
@@ -1059,7 +1060,17 @@ def test_maybe_allow_overruns_stream(
                 loglevel=loglevel,
                 debug_mode=debug_mode,
             )
-            seq = list(range(10))
+
+            # stream-sequence batch info with send delay to determine
+            # approx timeout determining whether test has hung.
+            total_batches: int = 2
+            num_items: int = 10
+            seq = list(range(num_items))
+            parent_send_delay: float = 0.16
+            timeout: float = math.ceil(
+                total_batches * num_items * parent_send_delay
+            )
+            with trio.fail_after(timeout):
                 async with portal.open_context(
                     echo_back_sequence,
                     seq=seq,
@@ -1075,7 +1086,6 @@ def test_maybe_allow_overruns_stream(
                         allow_overruns=(allow_overruns_side in {'parent', 'both'}),
                     ) as stream:
 
-                    total_batches: int = 2
                         for _ in range(total_batches):
                             for msg in seq:
                                 # print(f'root tx {msg}')
@@ -1084,7 +1094,7 @@ def test_maybe_allow_overruns_stream(
                                     # NOTE: we make the parent slightly
                                     # slower, when it is slow, to make sure
                                     # that in the overruns everywhere case
-                                await trio.sleep(0.16)
+                                    await trio.sleep(parent_send_delay)
 
                             batch = []
                             async for msg in stream:

tractor/msg/_codec.py

@@ -438,8 +438,8 @@ _ctxvar_MsgCodec: MsgCodec = RunVar(
     'msgspec_codec',
 
     # TODO: move this to our new `Msg`-spec!
-    # default=_def_msgspec_codec,
+    default=_def_msgspec_codec,
-    default=_def_tractor_codec,
+    # default=_def_tractor_codec,
 )