Update to Go 1.25 (#1018)

Update CI workflows to test against Go 1.24 and 1.25, and use Go 1.25 for
coverage and release builds.

## Benchstat Report: Go 1.24 vs Go 1.25

Benchmark comparison between Go 1.24.7 and Go 1.25.1 (10 runs each):

### Execution Time (sec/op)

| Benchmark | Go 1.24 | Go 1.25 | Delta |
|-----------|---------|---------|-------|
| UnmarshalDataset/config | 26.25ms | 26.00ms | ~ (p=0.280) |
| UnmarshalDataset/canada | 88.71ms | 84.94ms | **-4.26%** ✅ |
| UnmarshalDataset/citm_catalog | 33.71ms | 34.06ms | ~ (p=0.684) |
| UnmarshalDataset/twitter | 17.19ms | 17.33ms | ~ (p=0.971) |
| UnmarshalDataset/code | 107.4ms | 108.1ms | ~ (p=0.393) |
| UnmarshalDataset/example | 237.9µs | 251.3µs | +5.64% |
| Unmarshal/SimpleDocument/struct | 872.3ns | 848.9ns | ~ (p=0.165) |
| Unmarshal/SimpleDocument/map | 1.191µs | 1.278µs | +7.31% |
| Unmarshal/ReferenceFile/struct | 57.14µs | 57.95µs | ~ (p=0.089) |
| Unmarshal/ReferenceFile/map | 87.89µs | 92.88µs | +5.69% |
| Unmarshal/HugoFrontMatter | 16.06µs | 15.95µs | ~ (p=0.529) |
| Marshal/SimpleDocument/struct | 536.5ns | 563.5ns | +5.03% |
| Marshal/SimpleDocument/map | 651.0ns | 675.1ns | +3.72% |
| Marshal/ReferenceFile/struct | 44.63µs | 50.84µs | +13.91% |
| Marshal/ReferenceFile/map | 51.58µs | 57.06µs | +10.61% |
| Marshal/HugoFrontMatter | 10.04µs | 10.57µs | +5.27% |
| **geomean** | 140.6µs | 145.1µs | +3.18% |

### Summary

- Notable improvement: UnmarshalDataset/canada shows a 4.26% speedup
- Memory allocation and allocation counts remain identical
- Some marshal operations show slight slowdowns (likely Go runtime changes)

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

.github/workflows/coverage.yml

@@ -15,6 +15,6 @@ jobs:
       - name: Setup go
         uses: actions/setup-go@v6
         with:
-          go-version: "1.24"
+          go-version: "1.25"
       - name: Run tests with coverage
         run: ./ci.sh coverage -d "${GITHUB_BASE_REF-HEAD}"

.github/workflows/release.yml

@@ -22,7 +22,7 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v6
         with:
-          go-version: "1.24"
+          go-version: "1.25"
       - name: Login to GitHub Container Registry
         uses: docker/login-action@v3
         with:

.github/workflows/workflow.yml

@@ -12,7 +12,7 @@ jobs:
     strategy:
       matrix:
         os: [ 'ubuntu-latest', 'windows-latest', 'macos-latest', 'macos-14' ]
-        go: [ '1.23', '1.24' ]
+        go: [ '1.24', '1.25' ]
     runs-on: ${{ matrix.os }}
     name: ${{ matrix.go }}/${{ matrix.os }}
     steps: