perf(ci): enable incremental compilation for self-hosted Rust jobs

Change CARGO_INCREMENTAL from 0 to 1 for build and rust-tests jobs.
Self-hosted runners have persistent target/ directories, so incremental
compilation can reuse artifacts from previous runs for faster builds.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: pythoninthegrass

.github/workflows/test.yml

@@ -184,7 +184,7 @@ jobs:
     runs-on: self-hosted
     timeout-minutes: 5
     env:
-      CARGO_INCREMENTAL: 0  # Disable incremental compilation in CI (faster clean builds)
+      CARGO_INCREMENTAL: 1  # Enable incremental compilation on self-hosted (reuses artifacts)
       CARGO_TERM_COLOR: always
 
     steps:
@@ -218,7 +218,7 @@ jobs:
     needs: build
     timeout-minutes: 5
     env:
-      CARGO_INCREMENTAL: 0  # Disable incremental compilation in CI (faster clean builds)
+      CARGO_INCREMENTAL: 1  # Enable incremental compilation on self-hosted (reuses artifacts)
       CARGO_TERM_COLOR: always
 
     steps: