[Review] feat(boxsdkgen): add signer language, cancel sign request reason (box/box-openapi#584)

[govambam]

Recreated from box#1342 for Macroscope review.

Original PR: box#1342
Status: closed (merged)

Recreated using squash merge commit - exact merged state preserved.

Original PR: box#1342

[macroscopeapp]

Add signer language support and enable SignRequestsManager.cancelSignRequest to send an optional JSON reason payload in signRequests.ts

Introduce optional language on signer schemas and allow cancelSignRequest to include a JSON body with a cancellation reason; update pagination JSDoc to warn about unreliable high offsets and recommend marker-based pagination.

📍Where to Start

Start with SignRequestsManager.cancelSignRequest in signRequests.ts, then review the new SignRequestCancelRequest schema in signRequestCancelRequest.ts and signer language handling in signRequestCreateSigner.ts.

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Macroscope summarized e4bdff3.