feat(arr): add opensubtitles.com subtitle provider

Searches by moviehash computed from the media file and by TMDB id
with season/episode for TV, ranks candidates through
arr_core::subs::rank, and downloads under a lazily-fetched user
token. The daily download cap (429/406) surfaces as Error::RateLimited
so the loop can show a queue state. Credentials come from config or
environment only; tests run against wiremock fixtures.

Cargo.lock

@@ -205,8 +205,15 @@ name = "arr-subs"
 version = "0.1.0"
 dependencies = [
  "arr-core",
+ "arr-parse",
+ "reqwest",
+ "serde",
+ "serde_json",
+ "tempfile",
  "thiserror",
  "tokio",
+ "tracing",
+ "wiremock",
 ]
 
 [[package]]