chore(build): reduce binary size

[wass3r]

low hanging fruit to reduce build artifact size. adds -tags nomsgpack which was added in the gin framework many years ago (https://github.com/gin-gonic/gin/pull/2703/changes) to exclude msgpack functionality and its dependencies. we don't use msgpack, so it should be safe to exclude.

this reduces the binary size between 6-9MB depending on build type, build times are also reduced by about 5s (23s -> 18s on my system - results may vary):

build type	before	after
regular	71MB	62MB
static	50MB	44MB

i also checked for other build tags but didn't see any.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 58.16%. Comparing base (fbe4720) to head (22bb021).

❌ Your project check has failed because the head coverage (58.16%) is below the target coverage (90.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1377   +/-   ##
=======================================
  Coverage   58.16%   58.16%           
=======================================
  Files         646      646           
  Lines       24931    24931           
=======================================
  Hits        14500    14500           
  Misses       9767     9767           
  Partials      664      664           

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