Remove dead code from act/ (#971)

Removes code that whole-program reachability analysis (`deadcode` from `golang.org/x/tools`) confirmed unreachable, plus the `act/workflowpattern` package which no file outside its own directory imports.

- `act/common/draw.go` — CLI box-drawing helpers left over from nektos/act's dropped CLI
- `act/common/file.go` — `CopyFile`/`CopyDir` package-level helpers (container types have their own `CopyDir` methods, kept)
- `act/common/executor.go` — `Warning` type and `Warningf`. The `case Warning:` arm in `(Executor).Then`'s type switch was dead too (no code ever constructed a `Warning`); the switch is replaced with `if err != nil { return err }`
- `act/lookpath/env.go` — `LookPath` no-arg wrapper and `defaultEnv` struct. Only `LookPath2(file, env)` was used externally; the `Env` interface is kept
- `act/runner/action_cache_offline_mode.go` — `GoGitActionCacheOfflineMode` wrapper, never instantiated
- `act/workflowpattern/` — entire package, never imported

Net `-943` lines.

---
This PR was written with the help of Claude Opus 4.7

---------

Co-authored-by: Nicolas <bircni@icloud.com>
Reviewed-on: https://gitea.com/gitea/runner/pulls/971
Reviewed-by: Nicolas <bircni@icloud.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-committed-by: silverwind <me@silverwind.io>

act/common/executor.go

@@ -12,24 +12,6 @@ import (
 	log "github.com/sirupsen/logrus"
 )
 
-// Warning that implements `error` but safe to ignore
-type Warning struct {
-	Message string
-}
-
-// Error the contract for error
-func (w Warning) Error() string {
-	return w.Message
-}
-
-// Warningf create a warning
-func Warningf(format string, args ...any) Warning {
-	w := Warning{
-		Message: fmt.Sprintf(format, args...),
-	}
-	return w
-}
-
 // Executor define contract for the steps of a workflow
 type Executor func(ctx context.Context) error
 
@@ -162,14 +144,8 @@ func NewParallelExecutor(parallel int, executors ...Executor) Executor {
 // Then runs another executor if this executor succeeds
 func (e Executor) Then(then Executor) Executor {
 	return func(ctx context.Context) error {
-		err := e(ctx)
-		if err != nil {
-			switch err.(type) {
-			case Warning:
-				Logger(ctx).Warning(err.Error())
-			default:
-				return err
-			}
+		if err := e(ctx); err != nil {
+			return err
 		}
 		if ctx.Err() != nil {
 			return ctx.Err()