feat(go-ci): warm the build cache before linting, and let callers set the timeout

[juicycleff]

golangci-lint typechecks the whole module while it loads packages. With nothing
in GOCACHE that can outrun the deadline before a single linter runs, and the
failure names neither the repo nor the cause:

context loading failed: failed to load packages: context deadline exceeded

foundry hits this on every run. twinos already carries the same fix inline, so
this moves it somewhere the other consumers get it too.

What changed

The lint job builds the module before linting, which fills GOCACHE so package
loading reuses the compiled output instead of typechecking from scratch.

That step is continue-on-error: true on purpose. A module that genuinely does
not compile should be reported by golangci-lint, with a file and a line, rather
than as a bare build failure in a step the caller never asked for. So this
warms the cache and never changes whether the job passes.

golangci-lint-timeout exposes the deadline, defaulting to the 5m that was
hardcoded before. Warming the cache addresses the usual cause, so the input is
for repos where linting itself is honestly slow, not a way to paper over a cold
start. Existing callers see no change from either half.

Checked

actionlint is clean. The self-test smoke jobs exercise the lint path on the
fixtures, so the warm step gets a run here before any consumer sees it.