★ Exercise: a panic becomes an error

Write func safeCall(f func()) (err error). It calls f. When f panics, safeCall returns an error whose text is panic: <the panic value> — the value printed the way fmt.Println prints it. When there was no panic, safeCall returns nil.

• safeCall(func() {}) → nil
• safeCall(func() { panic("boom") }) → the error panic: boom
• safeCall(func() { panic(42) }) → the error panic: 42

Constraints: f is called exactly once; the panic value may be anything — a string, a number, an error, or Go's own panic such as an index out of range; after a recovered panic the next safeCall works as usual.

Do not add extra imports unless the task says so explicitly.