fix: reject NFT coins on FT APIs

[0Tech]

Description

This patch renames validateCoins() into validateFTCoins() and update its logic to reject valid NFT coins.

Motivation and context

validateCoins() are only used on FT APIs, but does not reject NFT coins. This patch addresses the problem.

Checklist:

• I followed the contributing guidelines and code of conduct.
• I have added a relevant changelog to CHANGELOG.md
• I have added tests to cover my changes.
• I have updated the documentation accordingly.
• I have updated API documentation client/docs/swagger-ui/swagger.yaml

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.42%. Comparing base (e86b980) to head (2aacdd0).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1294   +/-   ##
=======================================
  Coverage   70.42%   70.42%           
=======================================
  Files         643      643           
  Lines       54702    54702           
=======================================
  Hits        38526    38526           
  Misses      14006    14006           
  Partials     2170     2170           

Files	Coverage Δ
x/collection/msgs.go	98.31% <100.00%> (ø)