fix(context): Copy() copies Errors and Accepted fields

[Amirhf1]

Copy() now copies the Errors slice so goroutines receiving a copy can observe errors attached before the copy was made.
Copy() now copies the Accepted slice so content-negotiation state set by middleware (via SetAccepted) is preserved in the copy.
Both fields use independent slices — mutations on the copy do not affect the original context.

Context.Copy() was explicitly copying Keys and Params but
omitted Errors and Accepted, leaving them as nil in the copied
context regardless of the original's state.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.38%. Comparing base (3dc1cd6) to head (141ddaa).
⚠️ Report is 281 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4695      +/-   ##
==========================================
- Coverage   99.21%   98.38%   -0.83%     
==========================================
  Files          42       48       +6     
  Lines        3182     3166      -16     
==========================================
- Hits         3157     3115      -42     
- Misses         17       42      +25     
- Partials        8        9       +1     

Flag	Coverage Δ
	?
--ldflags="-checklinkname=0" -tags sonic	98.37% <100.00%> (?)
-tags go_json	98.31% <100.00%> (?)
-tags nomsgpack	98.36% <100.00%> (?)
go-1.18	?
go-1.19	?
go-1.20	?
go-1.21	?
go-1.25	98.38% <100.00%> (?)
go-1.26	98.38% <100.00%> (?)
macos-latest	98.38% <100.00%> (-0.83%)	⬇️
ubuntu-latest	98.38% <100.00%> (-0.83%)	⬇️

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