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/handler.go

@@ -427,8 +427,10 @@ func (h *Handler) reserve(w http.ResponseWriter, r *http.Request, _ httprouter.P
 		return
 	}
 
-	cache := api.ToCache()
-	cache.Repo = cred.Repo
+	cache := &Cache{Repo: cred.Repo, Key: api.Key, Version: api.Version, Size: api.Size}
+	if cache.Size == 0 {
+		cache.Size = -1
+	}
 	db, err := h.openDB()
 	if err != nil {
 		h.responseJSON(w, r, 500, err)