build(deps): run on gpui-fast instead of the gpui-pre snapshots

[Tryanks]

Change

• The root [patch.crates-io] points gpui-pre, -macros, -platform, -reqwest-client, -sum-tree and -web at gpui-fast's compat crates. GPUI Kit and Tcode now resolve to the same gpui-fast gpui. The crate declarations in the workspace are unchanged.
• gpui-fast has no gpui-pre-wgpu stand-in, so gpui-ios and gpui-android depend on gpui-fast's gpui_wgpu directly. Its WgpuRenderer::gpu_specs returns GpuSpecs rather than Option, and both backends wrap the result.
• ReqwestClient::from takes gpui-fast's zed-reqwest client, so tcode-ui builds that same client (same rev, still rustls-tls-webpki-roots).
• Cargo.lock keeps gpu-allocator on windows 0.62, as on main. Resolving gpui-fast had moved it to 0.58, whose D3D12 types wgpu-hal 29 cannot pass on Windows.
• The backend READMEs and crate docs now name gpui-fast.

Tests adjusted to gpui-fast

gpui-fast draws a view again only when something marked it dirty. None of the test failures after the switch reflects a behaviour difference in the app. They came from two test-side assumptions:

• Reading debug_bounds from a frame that reused views. In test-support builds, gpui-fast keeps every debug bound of the previous frame in any frame that reuses a view. An element that is no longer painted is therefore still found: a dismissed toast, a hidden jump-to-latest pill (the chat view rendered it hidden), a palette row scrolled away, or a finished navigation page. The chat, shell, palette and overlay tests now draw full frames through one draw helper per test module. This replaces the eight identical closures in the chat tests.
• A spring on the wall clock. The flat sidebar's row spring runs on Instant::now(), which the test executor does not advance. On gpui-fast the spring keeps its state across a reorder, so rows are still moving when positions are read. The order test sets reduced motion.

Checks run (macOS arm64)

• cargo fmt --all --check, cargo clippy --workspace --all-targets --locked -- -D warnings, cargo machete: pass.
• cargo nextest run --workspace --locked: all pass. tcode-traverse transport tests sometimes time out at 20s on this machine; they don't depend on GPUI and pass on rerun.
• cargo check -p tcode-ios --target aarch64-apple-ios-sim --locked and cargo check -p tcode-web --target wasm32-unknown-unknown --locked with RUSTFLAGS=-D warnings: pass. wgpu-hal checks for x86_64-pc-windows-msvc.
• The desktop binary starts with a throwaway TCODE_DATA_DIR and stays running. It was not inspected visually, and the phone layout was not run on a device.

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