Fix profile crash

This fixes a crash that would occasionally occur when visiting profiles.

NdbTxn objects were being deinitialized on different threads from their
initialization, causing incorrect reference count decrements in thread-local
transaction dictionaries. This led to premature destruction of shared ndb_txn
C objects still in use by other tasks, resulting in use-after-free crashes.

The root cause is that Swift does not guarantee tasks resume on the same
thread after await suspension points, while NdbTxn's init/deinit rely on
thread-local storage to track inherited transaction reference counts.

This means that `NdbTxn` objects cannot be used in async functions, as
that may cause the garbage collector to deinitialize `NdbTxn` at the end
of such function, which may be running on a different thread at that
point, causing the issue explained above.

The fix in this case is to eliminate the `async` version of the
`NdbNoteLender.borrow` method, and update usages to utilize other
available methods.

Note: This is a rewrite of the fix in https://github.com/damus-io/damus/pull/3329

Note 2: This relates to the fix of an unreleased feature, so therefore no
changelog is needed.

Changelog-None
Co-authored-by: alltheseas <64376233+alltheseas@users.noreply.github.com>
Closes: https://github.com/damus-io/damus/issues/3327
Signed-off-by: Daniel D’Aquino <daniel@daquino.me>

nostrdb/UnownedNdbNote.swift

@@ -66,19 +66,6 @@ enum NdbNoteLender: Sendable {
         }
     }
     
-    /// Borrows the note temporarily (asynchronously)
-    func borrow<T>(_ lendingFunction: (_: borrowing UnownedNdbNote) async throws -> T) async throws -> T {
-        switch self {
-        case .ndbNoteKey(let ndb, let noteKey):
-            guard !ndb.is_closed else { throw LendingError.ndbClosed }
-            guard let ndbNoteTxn = ndb.lookup_note_by_key(noteKey) else { throw LendingError.errorLoadingNote }
-            guard let unownedNote = UnownedNdbNote(ndbNoteTxn) else { throw LendingError.errorLoadingNote }
-            return try await lendingFunction(unownedNote)
-        case .owned(let note):
-            return try await lendingFunction(UnownedNdbNote(note))
-        }
-    }
-    
     /// Gets an owned copy of the note
     func getCopy() throws -> NdbNote {
         return try self.borrow({ ev in