feat/error handler

[onerandomusername]

• feat: add initial error handler
• add some CheckFailure handling support
• fix: implement remaining UserInputErrors
• fix: title regex
• fix: add concurrency errors and cooldown error support
• fix: don't log CommandNotFound errors unless in a dev mode
• fix: handle bot missing permissions

[codecov[bot]]

Codecov Report

Merging #77 (144b008) into main (b5ab21f) will decrease coverage by 5.32%. The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main      #77      +/-   ##
==========================================
- Coverage   38.62%   33.29%   -5.33%     
==========================================
  Files          16       17       +1     
  Lines         769      892     +123     
  Branches      105      132      +27     
==========================================
  Hits          297      297              
- Misses        459      582     +123     
  Partials       13       13              

Impacted Files	Coverage Δ
modmail/extensions/utils/error_handler.py	0.00% <0.00%> (ø)

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[onerandomusername]

There is a fundamental issue with the botmissingpermissions error handling. In almost all send message cases, the bot will make a second case which will 100% fail.

The bot should check its cache or request the channel perms to see if it has send message perms. If it does, should also check for embed image permissions, and send a standard message of content if that fails.

if that is not a valid permission, the bot should see if it has add_reaction permissions and maybe add a :x: if it can.

[onerandomusername]

There is a fundamental issue with the botmissingpermissions error handling. In almost all send message cases, the bot will make a second case which will 100% fail.

The bot should check its cache or request the channel perms to see if it has send message perms. If it does, should also check for embed image permissions, and send a standard message of content if that fails.

if that is not a valid permission, the bot should see if it has add_reaction permissions and maybe add a :x: if it can.

This is implemented in 7f19996