Mirrorlist should deal with unmatched, slightly incorrect versions and multiple minors for one major

[jonathanspw]

This came up while releasing 9.5 - the mirror system currently cannot handle 9.5 and 9.4 being support versions at the same time because only one exists in the duplicated_versions mapping. This is a regression introduced by the kitten support PR.

Relevant points in code and errors:

https://github.com/AlmaLinux/mirrors/blob/mirrors_service/src/backend/api/handlers.py#L434
https://github.com/AlmaLinux/mirrors/blob/mirrors_service/src/backend/api/handlers.py#L434

/opt/mirror_service/src/backend/update_mirrors.py:272: DeprecationWarning: There is no current event loop
  loop = asyncio.get_event_loop()
Traceback (most recent call last):
  File "/opt/mirror_service/src/backend/update_mirrors.py", line 273, in <module>
    loop.run_until_complete(update_mirrors())
  File "/usr/lib64/python3.12/asyncio/base_events.py", line 684, in run_until_complete
    return future.result()
           ^^^^^^^^^^^^^^^
  File "/opt/mirror_service/src/backend/update_mirrors.py", line 269, in update_mirrors
    await task
  File "/opt/mirror_service/src/backend/update_mirrors.py", line 103, in update_mirrors_handler
    mirror_iso_uris = mirror_processor.get_mirror_iso_uris(
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/mirror_service/src/backend/api/mirror_processor.py", line 472, in get_mirror_iso_uris
    for arch in arches[base_version]:
                ~~~~~~^^^^^^^^^^^^^^
KeyError: '9.5'

The expected functionality is for versions without a mapping in duplicate_version to still attempt to map to a valid major.

For example:

9.2 should map to 9
9.1111 should map to 9
9.97234 should map to 9

These are all past-supported versions, or invalid minors, but we should map the pattern to the major where we can make reasonable assumptions.