Forgot to commit this files in an earlier cleanup PR.

This only touches code I am developing, so will probably self-merge

Kind of surprised how much a change there is here. Did not do any update
(eg, didn't `go get -u` anything)

We don't actually have any rules or behavior around this event type,
just need to handle it here to reduce false-positive error logging.

Will need to be paired with an update and deploy in another internal
repo, after this is merged.

Ran lexgen against the `atproto` repo today (2025-04-06). Need to do
this periodically as maintenance; also I thought some Ozone event
changes needed to be pulled in, but maybe not.

Made two manual changes:

- did not include the removal of deprecated event types on
`subscribeRepos` (handle, tombstone, etc). that will have a broad impact
on the `events/` package, which persists events to disk using those
types
- manually commented out a `_Profile` type in the ozone types. I think
this is related to an open union thing

The main motivation here is to not have `splitter` import from `bgs`; it
was only doing so for MetricsMiddleware.

This moves MetricsMiddleware out to new service-oriented util package
(not directly in `util/` because it depends on prometheus and echo), and
updates the trivial usage to that.

Not touching `cmd/relay/` because that is getting refactored in a
separate branch; and not touching `search/metrics.go` because it adds
"extra" labels.

This is older code for working with PLC, and resolving handles.

This doesn't touch the code itself, just moves out of `api/*.go` to
other packages, and then marks those packages as deprecated.

Having this in `api/*.go` was weird because everything else under `api/`
is codegen (lexgen).

This fixes a specific typo, and also uses the declared const in more
places (to avoid similar typos).

thanks @rafaelbsky for reporting!

make function comment match function name

Signed-off-by: pudongair <744355276@qq.com>

- removed a deadcode function
- removed lingering "bigsky" references"
- removed unused "MemPersister" (it is still in the top-level events
package)
- move settings (using gorm/db) and otel code out of main.go (makes
main.go shorter)
- group imports consistently
- replace some "BGS" terminology with "relay"
- update README