Improve performance of some opam list combination

[kit-ty-kate]

With master (f39739b):

$ time opam list --available --installable -s --all-version dune.2.9.1
dune.2.9.1
opam list --available --installable -s --all-version dune.2.9.1  54.60s user 0.60s system 99% cpu 55.278 total

With this PR:

$ time opam list --available --installable -s --all-version dune.2.9.1
dune.2.9.1
./opam list --available --installable -s --all-version dune.2.9.1  2.91s user 0.37s system 98% cpu 3.317 total

Incidently, this also makes OpamListCommand.filter correct. Previously it would simply ignore its ~base parameter if the request did not start with a And case

[kit-ty-kate]

For --conflicts-with we get a 3x improvement. E.g. with opam master (f39739b):

$ time opam list --installed --conflicts-with base-domains.base -s --all-version
js_of_ocaml-compiler.3.11.0
opam list --installed --conflicts-with base-domains.base -s --all-version  0.97s user 0.33s system 97% cpu 1.339 total

With this PR:

$ time ./opam list --installed --conflicts-with base-domains.base -s --all-version
js_of_ocaml-compiler.3.11.0
./opam list --installed --conflicts-with base-domains.base -s --all-version  0.39s user 0.05s system 96% cpu 0.461 total

[AltGr]

Seems good, thanks!