chore(deps): update chroma, regexp2 v2, replace dimiro1/reply (#37858)

- Update `github.com/alecthomas/chroma/v2` to `v2.25.0`.
- Migrate `github.com/dlclark/regexp2` to `/v2` (incorporates
https://github.com/go-gitea/gitea/pull/37664); drop the renovate pin.
- Replace the unmaintained `github.com/dimiro1/reply` (the last consumer
of `regexp2` v1 in our own code) with a small built-in reply parser for
incoming mail.

Signed-off-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Claude (Opus 4.7) <noreply@anthropic.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Giteabot <teabot@gitea.io>
Co-authored-by: Nicolas <bircni@icloud.com>

renovate.json5

@@ -43,10 +43,6 @@
       "matchPackageNames": ["github.com/urfave/cli/v3"],
       "allowedVersions": "<3.6.2", // v3.6.2 breaks -c flag parsing in help commands
     },
-    {
-      "matchPackageNames": ["github.com/dlclark/regexp2"],
-      "allowedVersions": "^1", // v2 fails to build on linux/386: https://github.com/dlclark/regexp2/issues/102
-    },
     {
       "matchPackageNames": ["github.com/Azure/azure-sdk-for-go/sdk/azcore"],
       "allowedVersions": "<1.21.0", // v1.21.0+ uses API version unsupported by Azurite in CI