refactor: remove unreachable runner code (#1179)

Remove inherited act APIs, configuration branches, and test seams that neither the daemon nor exec can reach. Constant-fold settings both entry points already enforce and consolidate duplicate runner paths.

Major removals:

- Unwired custom action-cache and local-repository-cache implementations.
- Legacy matrix, platform, input, container-reuse, logging, Git remote, and action-replacement configuration paths.
- Unused Docker socket, container network, tar-copy, and platform PTY wrappers.
- Single-implementation filesystem, environment, runner, and expression abstractions.
- Duplicated step-container, command-logging, credential, reusable-workflow, and execution paths.
- Generated client mock boilerplate, obsolete fixtures, test-only seams, stale wrappers, and commented-out code.

This removes 2844 net Go lines while retaining Gitea RPC, event, matrix, input, cache, artifact, action, reusable workflow, Docker, host, exec, and release behavior.

Assisted by Codex (GPT-5).

Reviewed-on: https://gitea.com/gitea/runner/pulls/1179
Reviewed-by: bircni <bircni@icloud.com>
Co-authored-by: silverwind <me@silverwind.io>

act/artifactcache/model.go

@@ -10,23 +10,6 @@ type Request struct {
 	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"`
 	Repo      string `json:"repo" boltholdIndex:"Repo"`