feat: Prevent parallel delivery of same sender msgs

[byte-bandit]

Related Github tickets

• https://github.com/VolumeFi/paloma/issues/1760

Background

This change prevents multiple messages from the same sender to be relayed in parallel, even by different relayers. This is a preliminary security step for pigeon feed to prevent exploitable race conditions.

There's also some house keeping and tidying around the filtering logic.

Testing completed

• [x] test coverage exists or has been added/updated
• [x] tested in a private testnet

Breaking changes

• [x] I have checked my code for breaking changes
• [x] If there are breaking changes, there is a supporting migration.

[taariq]

@byte-bandit signed commit still an issue on this one. curious.