feat: token name & symbol return Option

[Daanvdplas]

The psp22 standard returns an Option<String>. In stead of having the contract needing to add additional logic, we handle it in the pallet.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 51.50%. Comparing base (5021c2f) to head (9b1d98c).
Report is 1 commits behind head on main.

@@            Coverage Diff             @@
##             main     #312      +/-   ##
==========================================
+ Coverage   51.47%   51.50%   +0.02%     
==========================================
  Files          48       48              
  Lines        4894     4897       +3     
  Branches     4894     4897       +3     
==========================================
+ Hits         2519     2522       +3     
  Misses       2326     2326              
  Partials       49       49              

Files with missing lines	Coverage Δ
pallets/api/src/fungibles/mod.rs	92.97% <100.00%> (+0.07%)	⬆️
pallets/api/src/fungibles/tests.rs	99.69% <100.00%> (+<0.01%)	⬆️

[chungquantin]

Some nitpitcks but not very important.

[evilrobot-01]

Looks good, made some minor suggestions for improving the tests which are quick and easy to implement if you so choose.