Add per-song update lock, retry with rate limit handling, token refreshing, and fix bug with logged index

[EffakT]

This PR introduces several improvements and fixes.

Features

Per-song Update Lock

• Added a locking mechanism per song to prevent redundant updates & request to spotify API.
• Lock duration has a 24hr jitter to prevent a stampede.
• Lock duration is configurable via argument -d.
• Specifying a lock duration of 0 will force an update.

Token Refreshing

• Spotify tokens expire after 60 minutes.
• Implemented automatic token refreshing 1minute before the token expires
• This ensures the Spotify token is always valid, and doesn't crash due to invalid token.

Retry with Rate Limit Handling

• Added retry logic for Rate Limited requests, Spotify Errors, and Timeouts.
• This includes exponential backoff, and respecting the Retry-After header returned by Spotify

Bug Fixes

Output Index Fix

• Corrects the output index with using the --start argument.
• Ensures that the displayed index reflects the correct global position.

Notes

• The locking allows the script to be re-run multiple times, only updating what is required, which is useful for libraries that are regularly updated.
• Retry and token refresh logic improves resilience against Spotify's API

Related Issues

resolves #9 resolves #8 partially #3

[quimnut]

the lock file needs logs/ prepended to land in a docker volume, lock feature fails silently when run in a container as is.

other features working great, thank you.

[EffakT]

the lock file needs logs/ prepended to land in a docker volume, lock feature fails silently when run in a container as is.

other features working great, thank you.

Thanks for letting me know, I don't really use docker much so didn't realize the lock couldn't be in the root. I've moved the lock file to the logs dir.