fix: Add fullPath in context copy

[KarthikReddyPuli]

Summary

When a gin.Context was copied using the Copy method, fullPath was not getting copied to the new context. This PR fixes it by copying the fullPath to the new context

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 99.36%. Comparing base (3dc1cd6) to head (3166ecd). Report is 10 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3784      +/-   ##
==========================================
+ Coverage   99.21%   99.36%   +0.15%     
==========================================
  Files          42       43       +1     
  Lines        3182     2677     -505     
==========================================
- Hits         3157     2660     -497     
+ Misses         17        9       -8     
  Partials        8        8              

Flag	Coverage Δ
	?
-race	∅ <ø> (?)
-tags "sonic avx"	99.35% <100.00%> (?)
-tags go_json	99.35% <100.00%> (?)
-tags nomsgpack	99.35% <100.00%> (?)
go-1.18	99.29% <100.00%> (+0.17%)	:arrow_up:
go-1.19	99.36% <100.00%> (+0.15%)	:arrow_up:
go-1.20	99.36% <100.00%> (+0.15%)	:arrow_up:
go-1.21	99.36% <100.00%> (+0.15%)	:arrow_up:
go-1.22	99.36% <100.00%> (?)
macos-latest	99.36% <100.00%> (+0.15%)	:arrow_up:
ubuntu-latest	99.36% <100.00%> (+0.15%)	:arrow_up:

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[KarthikReddyPuli]

@appleboy can you please review and merge this PR ?

[appleboy]

@KarthikReddyPuli Please help to fix conflcts.