Inline `send_yield` body to drop its deprecation

`experimental._pubsub`'s `fan_out_to_ctxs()` pushed each packet
via the now-deprecated `Context.send_yield()`, tripping its own
`DeprecationWarning` on every published msg.

Inline that method's exact body —
`await ctx.chan.send(Yield(cid=ctx.cid, pld=payload))` — so the
wire msg stays byte-identical (still a `Yield`) yet no warning
fires. The "proper" fix (swap to `MsgStream.send()` via
`Context.open_stream()`) needs BOTH sides migrated: the
subscriber still uses the legacy `Portal.open_stream_from()`
which never calls `.started()`, so a publisher-side
`open_stream()` raises a `RuntimeError` ("`started()` must be
called before opening a stream") — verified. Left as the
module's standing rework TODO.

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

tractor/experimental/_pubsub.py

@@ -38,6 +38,7 @@ import wrapt
 
 from ..log import get_logger
 from .._context import Context
+from ..msg import Yield
 
 
 __all__ = ['pub']
@@ -88,7 +89,18 @@ async def fan_out_to_ctxs(
             if ctx_payloads:
                 for ctx, payload in ctx_payloads:
                     try:
-                        await ctx.send_yield(payload)
+                        # NOTE: inline the (now-deprecated)
+                        # `Context.send_yield()` body to drop its
+                        # `DeprecationWarning` without a behaviour change.
+                        # The "proper" fix is migrating BOTH sides to
+                        # `open_context()`/`open_stream()`, but the
+                        # subscriber still uses the legacy
+                        # `Portal.open_stream_from()` (no `started()`
+                        # handshake) so `Context.open_stream()` can't be
+                        # used here yet — see this module's rework TODO.
+                        await ctx.chan.send(
+                            Yield(cid=ctx.cid, pld=payload)
+                        )
                     except (
                         # That's right, anything you can think of...
                         trio.ClosedResourceError, ConnectionResetError,