Refactor/java datetime alignment

[ozgliderpilot]

NB: This PR should be reviewed after #96 is reviewed and merged as it is stacked on it.

This implements the general java + mongo recommendations:

• Use Instant + BSON DateTime as the default for persisted timestamps and business events that care about "when did this happen?"
• Use LocalDate for "date only" concepts
• Use LocalTime for recurring "time-of-day only" rules
• Use LocalDateTime for human-scheduled local events (especially far-future appointments) and policies defined in local wall-clock terms, stored alongside an explicit ZoneId when you ultimately need a real instant

It also improves the integration test making it part of CICD with the test containers.

[cbullinger]

Can we add a new test for a round-trip of the released field through MongoDB; i.e. verify the released BSON values don't shift when read as LocalDate? probably fine for this dataset, but just a sanity check

Otherwise, this all looks great.

[cbullinger]

This is great! Just a comment on the dead testcontainers.version property, but otherwise LGTM!