[roll] Roll fuchsia [fxfs] Reduce the size futures with guards

Rust futures generated from async move {} blocks are at least double the
size of all captured variables:
rust-lang/rust#108906

There are 3 locations in fxfs where a future and a guard object are
captured inside of another future with the purpose of running the
original future while the guard is held. Rolling our own future for
this specific case halves the size of the outer futures.

This reduces the size of the future spawned in
FxFile::create_connection_async for prefetch_keys from 10032 bytes to
5024 bytes.

Original-Bug: b/393365596
Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1198687
Original-Revision: ec292e24290afb1d0aa96659f85075b6b23bbfbc
GitOrigin-RevId: f4b6749bb4fce66ec43aca06cf370f8cf6a3a9e3
Change-Id: I95c5034e44e2401253829efec2fa6ddadcdd37ba

Author: Chris Drouillard

stem

@@ -11,7 +11,7 @@
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-             revision="73c5a9cd01679095087457097081bcb74c6a3e7d"/>
+             revision="ec292e24290afb1d0aa96659f85075b6b23bbfbc"/>
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