fps: Enable gpui/profiler on the crate that uses it (#2823)

`gpui/profiler` is enabled on the workspace `gpui` dependency, so every
crate
in the workspace gets it. Only `gpui-fps` uses the feature —
`gpui::profiler`
appears in `crates/fps/src/lib.rs` and `crates/fps/src/sampler.rs` and
nowhere
else. `crates/base` has no reference to it at all.

Because cargo unifies features across the dependency graph, that
workspace-level
enablement reaches every downstream consumer too. A project that depends
only on
`gpui-base` still compiles gpui's profiler, and cannot turn it off from
its own
manifest — `default-features = false` on the consumer side does not
help,
because the feature is requested here.

That is currently a hard build failure on `wasm32-unknown-unknown`.
Against zed
`6e2fae61` (main at time of writing), gpui's profiler module does not
compile for
wasm32 — it mixes `std::time::Instant` with `web_time::Instant`:

```
error[E0308]: mismatched types
  --> crates/gpui/src/profiler/hang.rs:315
error[E0308]: `match` arms have incompatible types
  --> crates/gpui/src/profiler/journal.rs:87
  --> crates/gpui/src/profiler/journal.rs:99
error[E0308]: mismatched types
  --> crates/gpui/src/profiler.rs:1002
  --> crates/gpui/src/profiler.rs:1003
error: could not compile `gpui` (lib) due to 5 previous errors
```

The underlying gpui bug is zed's to fix, but a wasm consumer of
`gpui-base` has
no way to route around it while the feature is enabled workspace-wide.
Moving the
feature to the one crate that needs it makes the browser build work
today, and is
the right ownership regardless.

## Change

Drop `features = ["profiler"]` from the workspace `gpui` dependency and
set it on
`gpui-fps`, the only crate that uses it.

## Verification

Resolved feature sets, via `cargo tree -e features`:

| | `gpui-base` (wasm32) | `gpui-fps` |
|---|---|---|
| before | profiler **on** | on |
| after  | profiler **off** | **on** |

So the HUD is unaffected, and `story` still gets the feature
transitively through
its `gpui-fps` dependency.

Not verified: I did not run the full test suite or a complete workspace
build.
The change is limited to feature placement in two manifests, with no
source
changes and no public API change, so there is no `Breaking Changes`
section.

The one behavioural change for downstream users: anyone who was relying
on
`gpui/profiler` being enabled transitively via `gpui-base` or
`gpui-component`
will now need to enable it themselves, or depend on `gpui-fps`.

---

Parts of this PR were drafted with AI assistance (Claude). The
diagnosis, the
feature-resolution comparison, and the wording were reviewed by me.