fix: make service ready timeout configurable via env var

The DefaultServiceTimeout constant is hard-coded to 5 seconds, which
causes the inspect-server (and occasionally other services) to be killed
by the supervisor before they finish initialising on slow or
resource-constrained environments such as fly.io.

Replace the constant with a package-level var that reads
CARTESI_SERVICE_READY_TIMEOUT from the environment at process start.
The value must be a valid Go duration string (e.g. "30s", "1m").
If the variable is absent or invalid the original 5-second default is
preserved, so the change is fully backward-compatible.

Tested on fly.io: inspect-server takes ~21 s to become ready; with
CARTESI_SERVICE_READY_TIMEOUT=30s all services report ready and the
node runs normally.

Author: jplgarcia

internal/services/supervisor.go

@@ -7,12 +7,22 @@ import (
 	"context"
 	"errors"
 	"log/slog"
+	"os"
 	"time"
 
 	"golang.org/x/sync/errgroup"
 )
 
-const DefaultServiceTimeout = 5 * time.Second
+const defaultServiceTimeoutSeconds = 5
+
+var DefaultServiceTimeout = func() time.Duration {
+	if v := os.Getenv("CARTESI_SERVICE_READY_TIMEOUT"); v != "" {
+		if d, err := time.ParseDuration(v); err == nil && d > 0 {
+			return d
+		}
+	}
+	return defaultServiceTimeoutSeconds * time.Second
+}()
 
 var (
 	ServiceTimeoutError    = errors.New("timed out waiting for service to be ready")