The future goal is to enable manual patches to the completion files, instead of using clap_complete
directly. We can use clap_complete during development, but the end user doesn't need it anymore
(saving on compile time and binary size).

This is what we already did before the refactor with optional clap_complete.

My original approach was to use walkdir to list the packages, but
 * It requires some configuration/heuristic to find the repos
 * It adds a dependency on `walkdir` (though I could have reimplemented it locally)
 * It's actually slower than reading `emerge.log` (with 18k merges, and just the gentoo repo)
 * Not listing packages that have never been merged seems like a nicer behaviour

Making use of this in shell completion is a work in progress, but the Rust part looks done. Tweaked
docs too.

Fixes build on nightly.
rust-lang/rust#125319

Most users install those files via the ebuild, and the others can ignore the files, or grab them
from other sources. This simplifies the UI, and reduces the binary size by ~30k.

* Add completion for ebuild names
* Add docstrings for many enums
* Reduce redundant calls

Fish completions are really nice to write, maybe at the cost of flexibility: I couldn't figure out
how to easily complete on abbreviated commands, and I'm sometimes getting weird completions on
single-letter or unknown options.

* Add completion for ebuild names
* Add proper enum values
* Recognize/complete abbreviated commands
* Reduce redundant cases
* Ignore bash version < 4 (masked in gentoo)

Writing bash completions is more labor intensive, but looks less magical and ismore versatile (I got
closer to ideal completion than with fish). Not supporting docstrings is a real weak point though,
and the UI for selecting between a large number of options is meh.

* Add completion for ebuild names
* Ignore zsh version < 5.2 (not packaged in gentoo)

What a mess, zsh completion system is really complex, the docs is a wall of text, the tutorials
didn't help much. The clap-generated completion was buggy. This works better now, but is not as good
as bash and fish completions. I'm not a zsh user so I'll leave it at that, help welcome.

Bit of manual work needed to find that assert_cmd and predicates can't be updated due to
msrv. `cargo update -Zmsrv-policy` not doing its job ?

Removing adler v1.0.2
  Adding adler2 v2.0.0
Updating aho-corasick v1.1.2 -> v1.1.3
Updating anstream v0.6.13 -> v0.6.15
Updating anstyle v1.0.6 -> v1.0.8
Updating anstyle-parse v0.2.3 -> v0.2.5
Updating anstyle-query v1.0.2 -> v1.1.1
Updating anstyle-wincon v3.0.2 -> v3.0.4
Updating anyhow v1.0.80 -> v1.0.87
Updating autocfg v1.1.0 -> v1.3.0
Updating bstr v1.9.1 -> v1.10.0
Updating colorchoice v1.0.0 -> v1.0.2
Updating crc32fast v1.4.0 -> v1.4.2
Updating crossbeam-channel v0.5.12 -> v0.5.13
Updating crossbeam-utils v0.8.19 -> v0.8.20
Updating env_filter v0.1.0 -> v0.1.2
Updating env_logger v0.11.2 -> v0.11.5
Updating flate2 v1.0.28 -> v1.0.33
  Adding float-cmp v0.9.0
Updating hashbrown v0.14.3 -> v0.14.5
Updating indexmap v2.2.5 -> v2.5.0
  Adding is_terminal_polyfill v1.70.1
Updating itoa v1.0.10 -> v1.0.11
Updating libc v0.2.153 -> v0.2.158
Updating log v0.4.21 -> v0.4.22
Updating memchr v2.7.1 -> v2.7.4
Updating miniz_oxide v0.7.2 -> v0.8.0
  Adding normalize-line-endings v0.3.0
Updating num-traits v0.2.18 -> v0.2.19
Updating proc-macro2 v1.0.78 -> v1.0.86
Updating quote v1.0.35 -> v1.0.37
Updating regex v1.10.3 -> v1.10.6
Updating regex-automata v0.4.6 -> v0.4.7
Updating regex-syntax v0.8.2 -> v0.8.4
Updating ryu v1.0.17 -> v1.0.18
Updating serde v1.0.197 -> v1.0.210
Updating serde_derive v1.0.197 -> v1.0.210
Updating serde_json v1.0.114 -> v1.0.128
Updating serde_spanned v0.6.5 -> v0.6.7
Updating syn v2.0.52 -> v2.0.77
Updating thiserror v1.0.57 -> v1.0.63
Updating thiserror-impl v1.0.57 -> v1.0.63
Updating toml v0.8.10 -> v0.8.19
Updating toml_datetime v0.6.5 -> v0.6.8
Updating toml_edit v0.22.6 -> v0.22.20
Updating utf8parse v0.2.1 -> v0.2.2
Updating windows-targets v0.52.4 -> v0.52.6
Updating windows_aarch64_gnullvm v0.52.4 -> v0.52.6
Updating windows_aarch64_msvc v0.52.4 -> v0.52.6
Updating windows_i686_gnu v0.52.4 -> v0.52.6
  Adding windows_i686_gnullvm v0.52.6
Updating windows_i686_msvc v0.52.4 -> v0.52.6
Updating windows_x86_64_gnu v0.52.4 -> v0.52.6
Updating windows_x86_64_gnullvm v0.52.4 -> v0.52.6
Updating windows_x86_64_msvc v0.52.4 -> v0.52.6
Updating winnow v0.6.5 -> v0.6.18