Support for clap 4.4.6

[plugwash]

Hi.

In debian, we recently upgraded clap to version 4.4.6, since this was not a semver bump we were not expecting any breakage. Unfortunately it turns out it broke fd.

There are (at least) two issues, the first is that the "unstable-grouped" feature was remved in clap 4.2.0 by the commit clap-rs/clap@d5089b2 "fix!: Remove stablized unstable-grouped feature". By removing the reference to the "unstable-grouped" feature I was able to successfully build fd and run it's tests against clap versions 4.2.0 through 4.2.4.

The second issue arises starting with clap version 4.2.5, a bunch of tests fail with errors like.

---- test_custom_ignore_files stdout ----
thread 'test_custom_ignore_files' panicked at '`fd --ignore-file custom.ignore foo` did not exit successfully.
stdout:
---
---
stderr:
---
thread 'main' panicked at 'Command fd: Argument group 'execs' conflicts with non-existent 'has_results' id', /root/.cargo/registry/src/github.com-1ecc6299db9ec823/clap_builder-4.2.5/src/builder/debug_asserts.rs:317:13
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
---', tests/testenv/mod.rs:238:13

I'm not sure what should be done about this second issue.

[tmccombs]

I can look into this.