refactor(context): using maps.Clone

[cuiweixie]

https://go-review.googlesource.com/c/go/+/471400

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[cuiweixie]

name old time/op new time/op delta
MapClone-10 65.8ms ± 7% 10.3ms ± 2% -84.30% (p=0.000 n=10+9)

name old alloc/op new alloc/op delta
MapClone-10 40.2MB ± 0% 40.5MB ± 0% +0.57% (p=0.000 n=10+9)

name old allocs/op new allocs/op delta
MapClone-10 20.0 ± 0% 23.0 ± 0% +15.00% (p=0.000 n=10+10)

[haslam-forbes]

lol sorry ignore that please (i'm not a maintainer)

[Copilot]

Pull Request Overview

This PR refactors the Context.Copy() method to use Go's standard library maps.Clone function instead of manually copying map elements. This change simplifies the code by replacing a manual loop-based map copying approach with the built-in utility function.

• Replaced manual map copying logic with maps.Clone
• Added import for the maps package
• Removed the manual make and for loop for copying the Keys map

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[Copilot]

The maps.Clone call should be moved inside the mutex lock section. Currently, cKeys is read outside the lock but maps.Clone is called after acquiring the lock, which could lead to a race condition if c.Keys is modified between reading cKeys and cloning it.