fix(appcmd): use covariant collection types for choices

[shiftinv]

Summary

Updates the Choices type alias to use Sequence/Mapping instead of List/Dict respectively, which were invariant in their value type.
Type checkers would previously complain about commands.Param(choices=<list[str]>), expecting a list[str|int|float] instead.

While not technically supported before, choices=<tuple> used to work prior to 2.9 - see https://canary.discord.com/channels/808030843078836254/1177346079398838272.

Checklist

• If code changes were made, then they have been tested
  • I have updated the documentation to reflect the changes
  • I have formatted the code properly by running pdm lint
  • I have type-checked the code by running pdm pyright
• This PR fixes an issue
• This PR adds something new (e.g. new method or parameters)
• This PR is a breaking change (e.g. methods or parameters removed/renamed)
• This PR is not a code change (e.g. documentation, README, ...)