refactor: drop logrus and other direct dependencies (#1319)

After https://gitea.com/gitea/runner/pulls/1304, logrus stayed only to forward logs from docker/cli and moby/go-archive. The runner used a small part of those: volume parsing, the build context tar, the `ssh://` connection and registry credentials. Own code that matches them replaces them, so logrus leaves the module graph. docker/cli stays for its logrus-free `opts` and `connhelper/ssh` packages.

Other dependencies that the standard library or existing ones cover go too: mergo, httprouter (replaced by `http.ServeMux`), retry-go, go-isatty, go-selinux, container-device-interface, gotest.tools and go-cmp (replaced by testify). The binary shrinks by 5%.

Behaviour differences:

1. An unreadable file in a build context is skipped with a warning, where go-archive left a truncated tar.
2. Build contexts no longer carry `security.capability` xattrs.
3. The cache and artifact servers answer HEAD on GET routes, and no longer redirect trailing slashes or answer OPTIONS.

*Written by Claude.*

---------

Co-authored-by: bircni <[email protected]>
Reviewed-on: https://gitea.com/gitea/runner/pulls/1319
Reviewed-by: bircni <[email protected]>
Reviewed-by: Lunny Xiao <[email protected]>
Co-authored-by: silverwind <[email protected]>

DEVELOPMENT.md

@@ -33,7 +33,7 @@ depending on the prefix:
 
 ## Logging
 
-Log through `act/common/logging`; the linter rejects importing `log/slog` or logrus elsewhere.
+Log through `act/common/logging`; the linter rejects importing `log/slog` elsewhere.
 A job's logger comes from `common.Logger(ctx)`; code with no job uses the package functions
 (`logging.Infof`, `logging.With`). Both take printf-style messages, and `With("key", value)` adds
 fields.
@@ -43,11 +43,8 @@ fields.
 - The job logger's output can reach the job log workflow authors see, the process-wide logger's
   stays on the runner host, so keep operator-only detail (host paths, internal addresses) off the
   job logger.
-- Libraries that log through logrus's or slog's global logger are forwarded to the process-wide
-  one, so they follow its level and masking too.
-- That forwarding only works while logrus's global logger is left as `logging` configures it. A
-  dependency that calls `logrus.SetOutput` or `SetLevel` breaks it, so check
-  `logging.LogrusBridgeIntact()` when adding or upgrading one.
+- Libraries that log through slog's global logger are forwarded to the process-wide one, so they
+  follow its level and masking too. Avoid dependencies that log through logrus, nothing forwards it.
 - Tests read what was logged with `logtest.NewLogger()`, or `logtest.SetDefault(t)` for the
   package functions.