Stream token optimization for media object IIIF manifest endpoint

[cjcolvar]

Resolves #5476

There are two StreamToken methods at the heart of this PR:

• #purge_expired!
• #get_stream_tokens_for

In purge_expired! the first loop is avoided by using delete_all. The second loop is avoided by inverting the logic: finding the existing tokens in the DB instead of removing ones that no longer exist.

get_stream_tokens_for is a new batch alternative to find_or_create_session_token. This new method uses upsert_all to update existing records and create ones that do not exist yet. It takes a little bit of special handling to create the array of attribute hashes that upsert requires. Ids need to be added to that hash in order for upsert to find existing records without a unique index in the DB.

The rest of the PR is refactoring to utilize get_stream_tokens_for.

Future Work:

• Refactor playlist manifest endpoint to use optimized methods
• Remove unnecessary initialization of instance variables in media object view page (MediaObject#show setting up instance variables unnecessarily slowing down page #5477)

[Dananji]

Looks good to me as far as I understand 👍