ci: build the CI test wheel with a fast cargo profile

The release profile (lto=thin, codegen-units=1) is great for the shipped wheel
but slow to compile — it was the build-wheel long pole (~3m38s) gating the test
shards. Add [profile.ci] (no LTO, codegen-units=256, opt-level=1) and build the
CI wheel with --profile ci. Does not affect --release / shipped wheels.

.github/workflows/ci-fast.yml

@@ -62,10 +62,12 @@ jobs:
       - uses: Swatinem/rust-cache@v2
         with:
           workspaces: ". -> target"
-      - name: Build wheel once (maturin)
+      - name: Build wheel once (maturin, fast CI profile)
         run: |
           python -m pip install --upgrade pip maturin
-          maturin build --release --out dist --interpreter "python${PY_VERSION}"
+          # `--profile ci`: no LTO + parallel codegen-units → much faster compile
+          # than `--release` (lto + codegen-units=1). Tests don't need the optimized ext.
+          maturin build --profile ci --out dist --interpreter "python${PY_VERSION}"
       - uses: actions/upload-artifact@v4
         with:
           name: headroom-wheel

Cargo.toml

@@ -106,3 +106,16 @@ gcp_auth = "0.12"
 strip = "symbols"
 lto = "thin"
 codegen-units = 1
+
+# Fast-to-compile profile for CI test wheels. The shipped wheel uses
+# `release` (lto + codegen-units=1) for runtime/size; CI only needs a working
+# extension, so trade runtime perf for ~parallel, lto-free compilation. Used
+# via `maturin build --profile ci`. Does NOT affect `--release` builds.
+[profile.ci]
+inherits = "release"
+lto = false
+codegen-units = 256
+opt-level = 1
+strip = "none"
+debug = false
+incremental = false