search: New old search implementation (#39956)

This is an in-progress work on changing how task scheduler affects
performance of project search. Instead of relying on tasks being
executed at a discretion of the task scheduler, we want to experiment
with having a set of "agents" that prioritize driving in-progress
project search matches to completion over pushing the whole thing to
completion. This should hopefully significantly improve throughput &
latency of project search.

Release Notes:

- Improved project search performance

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Co-authored-by: Smit Barmase <smit@zed.dev>
Co-authored-by: Smit Barmase <heysmitbarmase@gmail.com>

crates/remote_server/Cargo.toml

@@ -75,7 +75,7 @@ minidumper.workspace = true
 
 [dev-dependencies]
 action_log.workspace = true
-agent.workspace = true
+agent = { workspace = true, features = ["test-support"] }
 client = { workspace = true, features = ["test-support"] }
 clock = { workspace = true, features = ["test-support"] }
 collections.workspace = true