Merge gitea/act into act/

Merges the `gitea.com/gitea/act` fork into this repository as the `act/`
directory and consumes it as a local package. The `replace github.com/nektos/act
=> gitea.com/gitea/act` directive is removed; act's dependencies are merged
into the root `go.mod`.

- Imports rewritten: `github.com/nektos/act/pkg/...` → `gitea.com/gitea/act_runner/act/...`
  (flattened — `pkg/` boundary dropped to match the layout forgejo-runner adopted).
- Dropped act's CLI (`cmd/`, `main.go`) and all upstream project files; kept
  the library tree + `LICENSE`.
- Added `// Copyright <year> The Gitea Authors ...` / `// Copyright <year> nektos`
  headers to 104 `.go` files.
- Pre-existing act lint violations annotated inline with
  `//nolint:<linter> // pre-existing issue from nektos/act`.
  `.golangci.yml` is unchanged vs `main`.
- Makefile test target: `-race -short` (matches forgejo-runner).
- Pre-existing integration test failures fixed: race in parallel executor
  (atomic counters); TestSetupEnv / command_test / expression_test /
  run_context_test updated to match gitea fork runtime; TestJobExecutor and
  TestActionCache gated on `testing.Short()`.

Full `gitea/act` commit history is reachable via the second parent.

Co-Authored-By: Claude (Opus 4.7) <noreply@anthropic.com>

act/artifactcache/model.go

@@ -0,0 +1,38 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// Copyright 2023 The nektos/act Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package artifactcache
+
+type Request struct {
+	Key     string `json:"key" `
+	Version string `json:"version"`
+	Size    int64  `json:"cacheSize"`
+}
+
+func (c *Request) ToCache() *Cache {
+	if c == nil {
+		return nil
+	}
+	ret := &Cache{
+		Key:     c.Key,
+		Version: c.Version,
+		Size:    c.Size,
+	}
+	if c.Size == 0 {
+		// So the request comes from old versions of actions, like `actions/cache@v2`.
+		// It doesn't send cache size. Set it to -1 to indicate that.
+		ret.Size = -1
+	}
+	return ret
+}
+
+type Cache struct {
+	ID        uint64 `json:"id" boltholdKey:"ID"`
+	Key       string `json:"key" boltholdIndex:"Key"`
+	Version   string `json:"version" boltholdIndex:"Version"`
+	Size      int64  `json:"cacheSize"`
+	Complete  bool   `json:"complete" boltholdIndex:"Complete"`
+	UsedAt    int64  `json:"usedAt" boltholdIndex:"UsedAt"`
+	CreatedAt int64  `json:"createdAt" boltholdIndex:"CreatedAt"`
+}