feat: add created_at and updated_at to wallets and accounts (#2177)

* feat: add `created_at` and `updated_at` to wallets and accounts

the title says it all :)

* fixup!

* nitpicks :)

* fixup!

* sqlite fix

* sqlite compat

* fixup!

* mypy

* revert db py

* motorinas suggestions

* int(time()) proper default values in migration

* uncomment migration

* use now = int(time()) idiom to make code more readable

also this fixes the issue where time() is called multiple times
providing different return values for multiple invocations

---------

Co-authored-by: Pavol Rusnak <pavol@rusnak.io>

lnbits/db.py

@@ -91,6 +91,12 @@ class Compat:
             return "(strftime('%s', 'now'))"
         return "<nothing>"
 
+    @property
+    def timestamp_column_default(self) -> str:
+        if self.type in {POSTGRES, COCKROACH}:
+            return self.timestamp_now
+        return "NULL"
+
     @property
     def serial_primary_key(self) -> str:
         if self.type in {POSTGRES, COCKROACH}: