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/state_cache/via.rs

@@ -81,7 +81,7 @@ pub async fn servers_route_via(&self, room_id: &RoomId) -> Result<Vec<OwnedServe
 pub fn servers_invite_via<'a>(
 	&'a self,
 	room_id: &'a RoomId,
-) -> impl Stream<Item = &ServerName> + Send + 'a {
+) -> impl Stream<Item = &'a ServerName> + Send + 'a {
 	type KeyVal<'a> = (Ignore, Vec<&'a ServerName>);
 
 	self.db