feat(log): add Logger.Debugln, expand test coverage, update Go/CI (#21)

- Add missing Logger.Debugln method (package-level Debugln existed but
  Logger type lacked it)
- Replace empty test stubs with real tests for Debug, Debugf, Info,
  Infof, Print, Printf, Notice, Warn, Warnf, Error, Errorf, Panic,
  Panicf, Panicln
- Add tests for namespace filtering, multi-namespace clients,
  namespace registry, level storage, colorize, parseLevelString,
  Broadcast, matchesNamespace, fileInfo, Logger.Debugln,
  empty namespace default
- Update go.mod to Go 1.26.1
- Update CI to actions/checkout@v4, actions/setup-go@v5, Go 1.26,
  add -race flag, trigger on pull_request
- Fix stale CRUSH.md references (Go version, CI config, stderr bug)

.github/workflows/ci.yaml

@@ -1,23 +1,20 @@
 name: Go package
 
-on: [push]
+on: [push, pull_request]
 
 jobs:
   test:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: Set up Go
-        uses: actions/setup-go@v4
+        uses: actions/setup-go@v5
         with:
-          go-version: "1.25"
-
-      - name: Install dependencies
-        run: go get .
+          go-version: "1.26"
 
       - name: Build
         run: go build -v ./...
 
       - name: Test
-        run: go test -v ./...
+        run: go test -race -v ./...