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feat(fhircast): track each subscriber's events and confirm them (#10096)

* feat(fhircast): alias FHIRcast STU3 routes at /api/hub

Some subscribers, notably the OHIF DICOM viewer, hardcode `hub.url` to
`/api/hub`. Mount the STU3 router there as well, and allow CORS on it.

Form-encoded subscription requests already worked -- the global
`urlencoded({ extended: false })` parser keeps dotted keys literal, so
the body arrives in the same shape the validators expect. Covered by a
test rather than a code change.

Fixes #10035

Signed-off-by: Derrick Farris <derrick@medplum.com>

* feat(fhircast): track each subscriber's events and confirm them

The Hub kept no record of what a subscriber asked for: `hub.events` came
back empty in the connection confirmation, and every socket on a topic
received every event published to it.

Give each subscribe request its own endpoint and store
`{projectId, topic, events, version}` under it in Redis, leased for the
same hour as the access token. On connect the socket reads that record
and keeps the events in memory, so it can now:

- confirm with the real `hub.events` -- the four fields STU3 defines,
  plus the ones STU3 dropped for STU2 subscribers
- receive only the events it asked for, matched case-insensitively the
  way the Hub already lowercases a published event to route it;
  `heartbeat` and `syncerror` reach everyone
- be denied on its own when it unsubscribes, rather than taking down
  every other subscriber on the topic

Closes #10028
Closes #6788
Closes #10030

Signed-off-by: Derrick Farris <derrick@medplum.com>

* refactor(fhircast): address static analysis findings

Use `findLast` rather than `filter(...).pop()` to take the endpoint from
a subscription URL, and make the always-delivered event list a `Set`.

Signed-off-by: Derrick Farris <derrick@medplum.com>

* refactor(fhircast): expire the user topic with the lease constant

`getTopicForUser` hardcoded the same hour `FHIRCAST_LEASE_SECONDS` now
carries, alo... (continued)

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