Add Nix flake for mcrctl

Vendor dependencies and expose mcrctl binary via nix build.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

vendor/git.wntrmute.dev/kyle/mcdsl/config/duration.go

@@ -0,0 +1,37 @@
+package config
+
+import (
+	"fmt"
+	"time"
+)
+
+// Duration is a [time.Duration] that can be unmarshalled from a TOML string
+// (e.g., "30s", "5m"). go-toml v2 does not natively decode strings into
+// time.Duration, so this wrapper implements [encoding.TextUnmarshaler].
+//
+// Access the underlying time.Duration via the embedded field:
+//
+//	cfg.Server.ReadTimeout.Duration  // time.Duration value
+//
+// Duration values work directly with time functions that accept
+// time.Duration because of the embedding:
+//
+//	time.After(cfg.Server.ReadTimeout.Duration)
+type Duration struct {
+	time.Duration
+}
+
+// UnmarshalText implements encoding.TextUnmarshaler for TOML string decoding.
+func (d *Duration) UnmarshalText(text []byte) error {
+	parsed, err := time.ParseDuration(string(text))
+	if err != nil {
+		return fmt.Errorf("invalid duration %q: %w", string(text), err)
+	}
+	d.Duration = parsed
+	return nil
+}
+
+// MarshalText implements encoding.TextMarshaler for TOML string encoding.
+func (d Duration) MarshalText() ([]byte, error) {
+	return []byte(d.String()), nil
+}