[automations] Vesting Scheduler V2 final clean-up

[kasparkallas]

• remove a confusing overload
• add cliffPeriod to createAndExecute function for completeness sake
• unify & restrict visibility modifiers
• slight refactor with start date normalization to achieve pure mapper function
• slightly change log event semantics when doing single transfer for a claim
• some renamings
• more tests
• instead of ctx, pass sender
• reduce duplication with _getId

[github-actions[bot]]

Changelog Reminder

Reminder to update the CHANGELOG.md for any of the modified packages in this PR.

• [ ] CHANGELOG.md modified
• [ ] Double check before merge

[github-actions[bot]]

XKCD Comic Relif

Link: https://xkcd.com/1973