fix(Qobuz): restore missing GTIN check digits

[floze-the-genius]

Summary

• normalize legacy Qobuz UPC values that contain 13 payload digits but omit the GTIN-14 check digit
• preserve Qobuz identifiers that already have a valid GTIN checksum
• add focused regression coverage for both missing and valid check digits

Qobuz historically used the truncated UPC as the album ID for older releases. When that 13-digit value has an invalid checksum, this appends the calculated check digit before exposing it as the release GTIN. Valid identifiers are returned unchanged.

Fixes #228

Validation

Run with the repository CI version, Deno 2.4.5:

• deno fmt --check (179 files)
• deno lint (172 files)
• deno task check
• deno test --deny-net --allow-read --allow-env (37 passed, 598 steps)
• deno task build
• focused deno test -RE providers/Qobuz/mod.test.ts (28 steps)

[kellnerd]

Thank you for picking this up. I kind of left my feedback in #228 since I would like to confirm with the Qobuz experts what the proper solution should look like.