fix: escape command data the runner writes itself (#1120)

Command data is percent-escaped on the wire because Gitea's job log cannot carry a newline, and the renderer decodes it.

1. Unescaping iterated a map, so order was random per process: `%250A` decoded to a newline instead of a literal `%0A` about two runs in three. Now a precompiled `strings.NewReplacer`.
1. Escape the data of command lines the runner writes itself (`##[error]`, `::group::Run …`), so decoding returns the original text instead of mangling a `%`. Multi-line runner errors also get real line breaks instead of a literal `\n`.
1. Register secrets in escaped form too — one containing `%` reaches the log as `%25…` and was never masked.
1. Decode in `jobLogFormatter`, so `gitea-runner exec` matches the web view.

## Relation to the Gitea PR

https://github.com/go-gitea/gitea/pull/38659 makes the renderer decode command data. Point 2 is required by it; the rest stand alone. Either order works — until both land, a new runner on old Gitea shows `%25`, an old runner on new Gitea shows the mangling point 2 fixes.
Co-authored-by: bircni <bircni@icloud.com>
Reviewed-on: https://gitea.com/gitea/runner/pulls/1120
Reviewed-by: bircni <bircni@icloud.com>
Co-authored-by: silverwind <me@silverwind.io>

act/runner/command_test.go

@@ -214,3 +214,10 @@ func TestSaveState(t *testing.T) {
 
 	assert.Equal(t, "state-value", rc.IntraActionState["step"]["state-name"])
 }
+
+func TestEscapeCommandData(t *testing.T) {
+	a := assert.New(t)
+
+	a.Equal("a%25b%0Dc%0Ad%250A", escapeCommandData("a%b\rc\nd%0A"))
+	a.Equal("a%b\rc\nd%0A", UnescapeCommandData("a%25b%0Dc%0Ad%250A"))
+}