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/database/map/keys_from.rs

@@ -15,7 +15,7 @@ use crate::{
 pub fn keys_from<'a, K, P>(
 	self: &'a Arc<Self>,
 	from: &P,
-) -> impl Stream<Item = Result<Key<'_, K>>> + Send + use<'a, K, P>
+) -> impl Stream<Item = Result<Key<'a, K>>> + Send + use<'a, K, P>
 where
 	P: Serialize + ?Sized + Debug,
 	K: Deserialize<'a> + Send,
@@ -40,7 +40,7 @@ where
 pub fn keys_raw_from<'a, K, P>(
 	self: &'a Arc<Self>,
 	from: &P,
-) -> impl Stream<Item = Result<Key<'_, K>>> + Send + use<'a, K, P>
+) -> impl Stream<Item = Result<Key<'a, K>>> + Send + use<'a, K, P>
 where
 	P: AsRef<[u8]> + ?Sized + Debug + Sync,
 	K: Deserialize<'a> + Send,