refactor(logging): add a logging abstraction and move the job logger onto it (#1295)

Add `act/common/logging`: a printf-style `Logger` on a slog-shaped `Handler`, with a logrus-backed handler as the only backend, plus a `logtest` handler for tests. Move the job logger onto it: `common.Logger` returns `*logging.Logger`, the job log formatters and the `Reporter` hook become handlers, and composite step IDs travel in the context.

Logging is tightly coupled to logrus types (hooks, formatters, `Entry.Data`). Going through our own interface first lets the remaining call sites move over with unchanged behavior, and lets the backend be swapped for `log/slog` in one place afterwards. The global process logger and its masking formatter stay on logrus for now.

Assisted-by: Codet
Co-authored-by: bircni <[email protected]>
Reviewed-on: https://gitea.com/gitea/runner/pulls/1295
Reviewed-by: bircni <[email protected]>

act/common/logging/level.go

@@ -0,0 +1,53 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package logging
+
+import (
+	"fmt"
+	"strings"
+)
+
+// Level is a log severity. The values match log/slog, with Trace added below Debug.
+type Level int
+
+const (
+	LevelTrace Level = -8
+	LevelDebug Level = -4
+	LevelInfo  Level = 0
+	LevelWarn  Level = 4
+	LevelError Level = 8
+)
+
+func (l Level) String() string {
+	switch {
+	case l <= LevelTrace:
+		return "trace"
+	case l <= LevelDebug:
+		return "debug"
+	case l <= LevelInfo:
+		return "info"
+	case l <= LevelWarn:
+		return "warn"
+	default:
+		return "error"
+	}
+}
+
+// ParseLevel accepts every name logrus does. "fatal" and "panic" map to LevelError because
+// the Logger has no level above it.
+func ParseLevel(s string) (Level, error) {
+	switch strings.ToLower(s) {
+	case "trace":
+		return LevelTrace, nil
+	case "debug":
+		return LevelDebug, nil
+	case "info":
+		return LevelInfo, nil
+	case "warn", "warning":
+		return LevelWarn, nil
+	case "error", "fatal", "panic":
+		return LevelError, nil
+	}
+	return LevelInfo, fmt.Errorf("not a valid log level: %q", s)
+}