fix: Resolve Clippy CI failures from elided lifetime warnings

The latest Rust nightly compiler (2025-08-27) introduced the
elided-named-lifetimes lint which causes Clippy CI checks to fail
when an elided lifetime ('_) resolves to a named lifetime that's
already in scope.

This commit fixes the Clippy warnings by:
- Making lifetime relationships explicit where 'a is already in scope
- Keeping elided lifetimes ('_) in functions without explicit
  lifetime parameters
- Ensuring proper lifetime handling in the database pool module

Affected files (17 total):
- Database map modules: Handle, Key, and KeyVal references in get,
  qry, keys, and stream operations
- Database pool module: into_recv_seek function

This change resolves the CI build failures without changing any
functionality, ensuring the codebase remains compatible with the
latest nightly Clippy checks.

src/service/rooms/short/mod.rs

@@ -62,7 +62,7 @@ pub async fn get_or_create_shorteventid(&self, event_id: &EventId) -> ShortEvent
 pub fn multi_get_or_create_shorteventid<'a, I>(
 	&'a self,
 	event_ids: I,
-) -> impl Stream<Item = ShortEventId> + Send + '_
+) -> impl Stream<Item = ShortEventId> + Send + 'a
 where
 	I: Iterator<Item = &'a EventId> + Clone + Debug + Send + 'a,
 {