Support dest and gitflags in forge repo clone

[untitaker]

Fix #98

[andrew]

Thanks, this is the right shape and the -- guard on the server URL is preserved.

One thing before merging: the arg parsing is too permissive. forge repo clone o/r a b c silently uses a as the destination and drops b c, and forge repo clone o/r a b -- --bare drops b the same way. gh errors on extra positionals here and I think we should too. Relatedly, forge repo clone -- --depth 1 has dashIdx == 0 so args[0] (--depth) ends up as both repoArg and the first git flag, and the resulting resolve.Repo error is confusing.

Something like this after computing dashIdx would cover both:

positional := len(args)
if dashIdx != -1 {
    positional = dashIdx
}
if positional < 1 {
    return errors.New("repository argument required")
}
if positional > 2 {
    return fmt.Errorf("accepts at most 2 arg(s) before --, received %d", positional)
}

Then the two branches collapse to repoArg = args[0], if positional > 1 { dest = args[1] }, if dashIdx != -1 { gitFlags = args[dashIdx:] }.

Everything else looks good, the new gitCloneArgs test cases are exactly what I'd want.

[andrew]

Thanks