perf: optimize pointer bytes on mesgdef

[muktihari]

This PR will place any pointer bytes: slice, string and array of string at the beginning of the mesgdef's structs to reduce GC workload for scanning its pointers.

Ref: https://cs.opensource.google/go/x/tools/+/refs/tags/v0.44.0:go/analysis/passes/fieldalignment/fieldalignment.go;l=30-44

Pointer bytes is how many bytes of the
object that the garbage collector has to potentially scan for pointers, for example:

	struct { uint32; string }

have 16 pointer bytes because the garbage collector has to scan up through the string's
inner pointer.

	struct { string; *uint32 }

has 24 pointer bytes because it has to scan further through the *uint32.

	struct { string; uint32 }

has 8 because it can stop immediately after the string pointer.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (989716d) to head (65d8b55).
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #620   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           43        43           
  Lines         3771      3771           
=========================================
  Hits          3771      3771           

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