refactor(nexus)!: refactor to move coin locking unlocking logic from axelarnet to nexus

[fish-sammy]

• create nexus Coin struct
• pick up the new nexus Coin and remove axelarnet Coin

Description

Todos

• Unit tests
• Manual tests
• Documentation
• Connect epics/issues
• Tag type of change
• Upgrade handler

Steps to Test

Expected Behaviour

Other Notes

[codecov]

Codecov Report

Attention: Patch coverage is 36.06089% with 672 lines in your changes missing coverage. Please review.

Project coverage is 39.17%. Comparing base (6271ef5) to head (fd6776a).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
x/axelarnet/types/mock/expected_keepers.go	6.78%	506 Missing and 2 partials ⚠️
x/nexus/types/mock/expected_keepers.go	63.33%	80 Missing and 8 partials ⚠️
x/nexus/keeper/lockable_coin.go	69.52%	21 Missing and 11 partials ⚠️
x/nexus/exported/mock/types.go	72.00%	17 Missing and 4 partials ⚠️
x/axelarnet/module.go	36.36%	5 Missing and 2 partials ⚠️
x/axelarnet/keeper/msg_server.go	76.00%	5 Missing and 1 partial ⚠️
x/nexus/exported/types.go	0.00%	3 Missing ⚠️
x/nexus/module.go	0.00%	3 Missing ⚠️
x/axelarnet/handler.go	0.00%	2 Missing ⚠️
x/axelarnet/keeper/ibc_transfer.go	0.00%	1 Missing ⚠️
... and 1 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2186      +/-   ##
==========================================
- Coverage   39.89%   39.17%   -0.73%     
==========================================
  Files         373      373              
  Lines       30857    31676     +819     
==========================================
+ Hits        12310    12408      +98     
- Misses      17622    18331     +709     
- Partials      925      937      +12     

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[milapsheth]

I think this will break in-transit IBC transfers that timeout or have an ack error. Those packets were sent from the escrow accounts, and so the coin would be refunded back to the escrow and the locking here will fail as a result. We can explicitly check what the packet sender was to distinguish this behaviour. But could timeout/ack error be delayed indefinitely? In that case, we might always need to have this fallback