Fix missing stripeContext in RequestOptions.toBuilderFullCopy()

[IamPritamAcharya]

Why?

RequestOptions.toBuilderFullCopy() does not copy the stripeContext field,
causing it to be lost when rebuilding a RequestOptions instance.

This leads to unexpected behavior where request context metadata is silently dropped.

Before this change:
opts.toBuilderFullCopy().build().getStripeContext() == null

After this change:
opts.toBuilderFullCopy().build().getStripeContext() == original value

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What?

• Added .setStripeContext(this.stripeContext) in toBuilderFullCopy()
• Added a regression test to ensure stripeContext is preserved during copy

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See Also

• toBuilderFullCopy() does not copy all fields — stripeContext (and others) are missing #2205

Changelog

• Fixes a bug where an existing stripeContext was being reset to null when calling RequestOptions#toBuilderFullCopy()

[mbroshi-stripe]

Thanks for catching this and submitting a fix! I left a couple minor comments to address

[IamPritamAcharya]

@mbroshi-stripe
Addressed feedback:

• Removed redundant test
• Fixed formatting issues

Thanks for the review!