Return Option from Contact::add_or_lookup()

This allows to distinguish exceptions,
such as database errors, from invalid user input.
For example, if the From: field of the message
does not look like an email address, the mail
should be ignored. But if there is a database
failure while writing a new contact for the address,
this error should be bubbled up.

CHANGELOG.md

@@ -10,6 +10,8 @@
 ### Fixes
 - fix: only send contact changed event for recently seen if it is relevant (not too old to matter) #3938
 - Immediately save `accounts.toml` if it was modified by a migration from absolute paths to relative paths #3943
+- Do not treat invalid email addresses as an exception #3942
+
 
 ## 1.105.0