allowlist replace_in_metadata in yt_dlp_opts

[bradleesand]

What

Adds replace_in_metadata to _YTDLP_DOWNLOAD_ALLOWLIST so it can be passed via yt_dlp_opts in config.

Why

replace_in_metadata is a yt-dlp post-processor option that rewrites metadata fields using regex substitution (e.g. stripping remaster suffixes or channel name suffixes from titles). It doesn't affect the download itself — it only transforms metadata — so it's safe to allowlist alongside options like ratelimit and retries.

Without this, users who set replace_in_metadata in yt_dlp_opts have it silently dropped.

Test

Added a test to tests/test_ytdlp_download_opts.py verifying the option passes through build_ytdlp_opts for download operations.

[loganbuilt]

@bradleesand can you change this to merge into arr_integration branch? I'm about to release v1.0.0 from that branch and I do think this PR can go there cleanly! thanks

[bradleesand]

Sorry I missed the v1.0.0 release, the past two weeks have been extra busy for me. Congrats on shipping 1.0.0!

Rebased onto current main. Since arr_integration was merged into main as part of the release, I kept the base as main rather than retargeting — the change applies cleanly there. The only conflict was in CHANGELOG.md (release churn), now resolved with the note under a fresh ## Unreleased section at the top. The functional change is unchanged: replace_in_metadata added to _YTDLP_DOWNLOAD_ALLOWLIST, plus the passthrough test. pytest tests/test_ytdlp_download_opts.py passes (9/9).

[loganbuilt]

thank you!
I've been working on this for a while now. I've got alot of work to do on Music still. I'm interested in hearing your thoughts on where the project is at now. my email is listed on my profile page, if you want to get in touch with me, feel free! Good to have someone else jumping in on the project. Thanks