Modernize CI action versions (#67)

The CodeQL and golangci-lint workflows were pinned to action versions
that GitHub has retired:

- actions/checkout@v2 (Node 12-based, retired)
- github/codeql-action/{init,autobuild,analyze}@v1 (v1 retired by GitHub)
- golangci/golangci-lint-action@v2 (from 2021)

These jobs were either silently failing or running in degraded mode,
producing a false static-analysis signal on every PR.

Changes:

- Bump actions/checkout to @v6 (matches the existing ci.yml convention).
- Bump github/codeql-action/* to @V3 (current stable major).
- Bump golangci/golangci-lint-action to @v6.
- Pin golangci-lint to v1.62.0. 'version: latest' picks up new linters
  on every run, which can break unrelated PRs; a fixed version is
  deterministic and bumped intentionally.
- Add actions/setup-go@v6 to the lint workflow, reading the Go version
  from go.mod so the lint job exercises the same toolchain as the test
  job.

Closes #27

Co-authored-by: Claude <noreply@anthropic.com>

Author: dolph

.github/workflows/codeql-analysis.yml

@@ -25,16 +25,16 @@ jobs:
 
     steps:
     - name: Checkout repository
-      uses: actions/checkout@v2
+      uses: actions/checkout@v6
 
     # Initializes the CodeQL tools for scanning.
     - name: Initialize CodeQL
-      uses: github/codeql-action/init@v1
+      uses: github/codeql-action/init@v3
       with:
         languages: ${{ matrix.language }}
 
     - name: Autobuild
-      uses: github/codeql-action/autobuild@v1
+      uses: github/codeql-action/autobuild@v3
 
     - name: Perform CodeQL Analysis
-      uses: github/codeql-action/analyze@v1
+      uses: github/codeql-action/analyze@v3

.github/workflows/golangci-lint.yml

@@ -15,8 +15,12 @@ jobs:
     name: lint
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v6
+      - uses: actions/setup-go@v6
+        with:
+          go-version-file: go.mod
+          cache: true
       - name: golangci-lint
-        uses: golangci/golangci-lint-action@v2
+        uses: golangci/golangci-lint-action@v6
         with:
-          version: latest
+          version: v1.62.0