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

[govambam]

Recreated from box#1343 for Macroscope review.

Original PR: box#1343
Status: closed (merged)

Recreated using squash merge commit - exact merged state preserved.

Original PR: box#1343

[macroscopeapp]

Add signer language support and send cancel reason body in SignRequestsManager.cancelSignRequest for Box Sign requests

Add language to signer payloads and allow POST /2.0/sign_requests/{id}/cancel to include a JSON reason body, with updated pagination docs for folders.

📍Where to Start

Start with the cancelSignRequest flow in src/managers/signRequests.ts, then review schema changes in src/schemas/signRequestCancelRequest.ts and signer language handling in src/schemas/signRequestCreateSigner.ts.

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Macroscope summarized 9760d00.