Refactor database error handling across repositories to use IntoDbResult for improved error management

- Updated PgNotificationRepository to utilize IntoDbResult for error handling in various methods.
- Refactored PgRemoteActorRepository to replace manual error mapping with IntoDbResult.
- Modified PgRemoteActorConnectionRepository to implement IntoDbResult for error handling.
- Adjusted PgTagRepository to use IntoDbResult for consistent error management.
- Introduced test_helpers module for seeding users and thoughts in tests.
- Enhanced PgThoughtRepository to leverage IntoDbResult for error handling.
- Updated PgTopFriendRepository to utilize IntoDbResult for error management.
- Refactored PgUserRepository to implement IntoDbResult for error handling.
- Added constants for pagination defaults in requests.
- Introduced MAX_TOP_FRIENDS constant for top friends validation.
- Refactored JWT expiration time to use a constant.
- Improved rate limiter configuration with constants for better readability.
- Added utility methods for FollowState and Visibility enums for string conversions.
- Introduced maximum length constants for Username, Email, and Content value objects.
- Cleaned up test modules by removing redundant code and utilizing a shared testing state.

crates/application/src/use_cases/profile.rs

@@ -1,3 +1,5 @@
+const MAX_TOP_FRIENDS: usize = 8;
+
 use domain::{
     errors::DomainError,
     events::DomainEvent,
@@ -79,7 +81,7 @@ pub async fn set_top_friends(
     user_id: &UserId,
     friend_ids: Vec<UserId>,
 ) -> Result<(), DomainError> {
-    if friend_ids.len() > 8 {
+    if friend_ids.len() > MAX_TOP_FRIENDS {
         return Err(DomainError::InvalidInput("top friends: max 8".into()));
     }
     let friends: Vec<(UserId, i16)> = friend_ids