Fix mpdstats CLI option overrides

[Tsuizxgo]

Description

Fixes #5404.

The mpdstats command already overlays CLI options onto the mpd config with mpd_config.set_args(opts). After that, it tried to manually apply the same options again, which caused two problems on Python 3:

• --host and --password values are already strings, so calling .decode("utf-8") crashed.
• --port was accidentally assigned to mpd_config["host"], producing an invalid host configuration.

This change removes the redundant manual override block and relies on set_args() to preserve the correct option types.

To Do

• Documentation. This is a bug fix for existing CLI options.
• Changelog. Added an entry to docs/changelog.rst.
• Tests. Added regression coverage for CLI --host, --port, and --password overrides.

Tests

BEETSDIR=/private/tmp/beets-test-config UV_CACHE_DIR=/private/tmp/uv-cache uv run pytest test/plugins/test_mpdstats.py
# 4 passed

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.66%. Comparing base (52a7ba6) to head (cf7c5e4).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6699      +/-   ##
==========================================
+ Coverage   72.59%   72.66%   +0.06%     
==========================================
  Files         162      162              
  Lines       20811    20805       -6     
  Branches     3293     3290       -3     
==========================================
+ Hits        15107    15117      +10     
+ Misses       4980     4964      -16     
  Partials      724      724              

Files with missing lines	Coverage Δ
beetsplug/mpdstats.py	60.21% <ø> (+7.09%)	⬆️

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[snejus]

Can you rebase this on top of master? I don't seem to have permissions to do so.