style: gofmt all packages (#4)

Applies gofmt to the 18 files that were already unformatted at HEAD (pre-existing debt — 122 insertions / 122 deletions, whitespace plus import-block reorderings only; `git diff -w` confirms no semantic changes).

Kept on its own branch so the functional change set (see the review-hardening PR) stays reviewable without formatting noise.

Verified: go build, go vet, go test ./... pass on this branch; a merge simulation with the functional branch produces a clean 3-way merge with all tests green.
Reviewed-on: #4
Co-authored-by: David Gwilliam <dhgwilliam@gmail.com>
Co-committed-by: David Gwilliam <dhgwilliam@gmail.com>

internal/metrics/metrics_test.go

@@ -111,4 +111,4 @@ func TestMetricsCounters(t *testing.T) {
 	if got := testutil.ToFloat64(m.errorsTotal); got != 1 {
 		t.Errorf("errorsTotal = %v, want 1", got)
 	}
-}
+}