.data.feed: move `Flume` import to avoid cycle

Move `Flume` to `TYPE_CHECKING` and add runtime imports in
`allocate_persistent_feed()` + `open_feed()` to avoid cycle
with `.flows` mod.

(this commit msg was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code

piker/data/feed.py

@@ -62,7 +62,6 @@ from ._util import (
     log,
     get_console_log,
 )
-from .flows import Flume
 from .validate import (
     FeedInit,
     validate_backend,
@@ -77,6 +76,7 @@ from ._sampling import (
 )
 
 if TYPE_CHECKING:
+    from .flows import Flume
     from tractor._addr import Address
     from tractor.msg.types import Aid
 
@@ -362,6 +362,8 @@ async def allocate_persistent_feed(
     )
     await some_data_ready.wait()
 
+    # XXX, avoid cycle; it imports this mod.
+    from .flows import Flume
     flume = Flume(
 
         # TODO: we have to use this for now since currently the
@@ -500,7 +502,6 @@ async def open_feed_bus(
     sub_registered = trio.Event()
 
     flumes: dict[str, Flume] = {}
-
     for symbol in symbols:
 
         # if no cached feed for this symbol has been created for this
@@ -684,6 +685,7 @@ class Feed(Struct):
     '''
     mods: dict[str, ModuleType] = {}
     portals: dict[ModuleType, tractor.Portal] = {}
+
     flumes: dict[
         str,  # FQME
         Flume,
@@ -951,6 +953,8 @@ async def open_feed(
 
         assert len(feed.mods) == len(feed.portals)
 
+        # XXX, avoid cycle; it imports this mod.
+        from .flows import Flume
         async with (
             trionics.gather_contexts(bus_ctxs) as ctxs,
         ):