iOS: reject instead of crashing when an upload's file is missing

[dmurphy5]

This is a fix for the current version, not v10

On iOS, uploadTask(with:fromFile:) on a background session throws an Objective-C exception when it cannot read the file. Swift cannot catch that exception, so the app dies. In Diana this is Sentry DIANA-19VW: about 2,500 crashes from 1,700 users since August. It usually happens at launch. The app checks that the file exists, and then a finished upload deletes that file before iOS opens it.

This change wraps the call in a small Objective-C helper that catches the exception and returns it to Swift as an error.

Before: a missing file ends the app.
After: startUpload rejects with "Cannot read file at …". Any concurrent calls with the same id get the same rejection. A chunked part that cannot be enqueued stalls with errorKind: 'file'.

What to look at

• The podspec. RNBGUCatchException.h is now the one public header, so Swift can see it through the module umbrella. It imports only Foundation, so a plain Obj-C @import react_native_background_upload; still compiles.
• startUpload in RNBackgroundUpload.swift. Parked same-id calls now store both resolve and reject, so a failure reaches all of them.

Decisions and trade-offs

• A chunked part that fails to enqueue stalls. A failed part-file build is handled the same way. The upload keeps its bytes, and the next startUpload resumes it.
• The rejection uses the existing "RN Uploader" code. The thrown error is NSURLErrorCannotOpenFile, so errorKind(for:) classifies it as 'file'.
• Version 9.0.1 is set, but no tag is created. Tagging happens at release.

Test Plan

• A standalone macOS program created a background session and uploaded a missing file. It raised "NSInvalidArgumentException: Cannot read file at …", which matches the Sentry event. With the helper the exception was caught. Without it the process terminated.
• All iOS Swift sources type-check against the iOS 15.1 SDK, with React's two promise typedefs stubbed. Unmodified master also passes this check.
• yarn lint-root, yarn typecheck and yarn test pass with 37 tests.
• Not verified: a real CocoaPods build and a device run. Pod install must pick up the two new files and put the public header in the umbrella.

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