… returned error types

This is the last change from what was started with #1437. That PR introduced a few private error types, but for the errors returned in the public `APIs` we were still passing around `Error`s everywhere, which didn't provide any compile-time guarantees.

- Ensure that public APIs *only* return `ErrorCode`s wrapped with the additional `userInfo`, and not accidentally return other types like `SKError`, `BackendError`, `ErrorCode` directly, etc.
- Guarantee type-safety when passing errors around within our internal implementations instead of assuming certain thrown errors are of a particular type.

- Created `PurchasesError` for wrapping an `ErrorCode` with the additional `userInfo`.
- Changed returned errors from `Error` to `NSError`. This is a change in the API, but the new type is a more specific `Error` so it shouldn't lead to any changes in client apps.
- Because `PurchasesError` isn't implicitly convertible to `NSError`, this ensures that we don't return those values directly, and instead use `PurchasesError.asPublicError`.
- Changed `ErrorCodeConvertible` to a now more precise `PurchasesErrorConvertible`.

Thanks to this new type-safety this PR fixes at least 2 bugs where we were returning private errors instead of `ErrorCode`s.

Thanks to #1871 we know that the returned errors are still convertible to `ErrorCode` so users can `switch` over them.

… returned error types (#1879)

This is the last change from what was started with #1437. That PR introduced a few private error types, but for the errors returned in the public `APIs` we were still passing around `Error`s everywhere, which didn't provide any compile-time guarantees.

### Goals:
- Ensure that public APIs *only* return `ErrorCode`s wrapped with the additional `userInfo`, and not accidentally return other types like `SKError`, `BackendError`, `ErrorCode` directly, etc.
- Guarantee type-safety when passing errors around within our internal implementations instead of assuming certain thrown errors are of a particular type.

### Changes:
- Created `PurchasesError` for wrapping an `ErrorCode` with the additional `userInfo`.
- Changed returned errors from `Error` to `NSError`. This is a change in the API, but the new type is a more specific `Error` so it shouldn't lead to any changes in client apps.
- Because `PurchasesError` isn't implicitly convertible to `NSError`, this ensures that we don't return those values directly, and instead use `PurchasesError.asPublicError`.
- Changed `ErrorCodeConvertible` to a now more precise `PurchasesErrorConvertible`.

Thanks to this new type-safety this PR fixes at least 3 bugs where we were returning private errors instead of `ErrorCode`s.

### Testing:

Thanks to #1871 we know that the returned errors are still convertible to `ErrorCode` so users can `switch` over them.

**This is an automatic release.**

### Bugfixes
* `watchOS`: fixed crash when ran on single-target apps with Xcode 14 and before `watchOS 9.0` (#1895) via NachoSoto (@NachoSoto)
* `CustomerInfoManager`/`OfferingsManager`: improved display of underlying errors (#1888) via NachoSoto (@NachoSoto)
* `Offering`: improved confusing log for `PackageType.custom` (#1884) via NachoSoto (@NachoSoto)
* `PurchasesOrchestrator`: don't log warning if `allowSharingAppStoreAccount` setting was never explicitly set (#1885) via NachoSoto (@NachoSoto)
* Introduced type-safe `PurchasesError` and fixed some incorrect returned error types (#1879) via NachoSoto (@NachoSoto)
* `CustomerInfoManager`: fixed thread-unsafe implementation (#1878) via NachoSoto (@NachoSoto)
### New Features
* Disable SK1's `StoreKitWrapper` if SK2 is enabled and available (#1882) via NachoSoto (@NachoSoto)
* `Sendable` support (#1795) via NachoSoto (@NachoSoto)
### Other Changes
* Renamed `StoreKitWrapper` to `StoreKit1Wrapper` (#1886) via NachoSoto (@NachoSoto)
* Enabled `DEAD_CODE_STRIPPING` (#1887) via NachoSoto (@NachoSoto)
* `HTTPClient`: added `X-Client-Bundle-ID` and logged on SDK initialization (#1883) via NachoSoto (@NachoSoto)
* add link to SDK reference (#1872) via Andy Boedo (@aboedo)
* Added `StoreKit2Setting.shouldOnlyUseStoreKit2` (#1881) via NachoSoto (@NachoSoto)
* Introduced `TestLogHandler` to simplify how we test logged messages (#1858) via NachoSoto (@NachoSoto)
* `Integration Tests`: added test for purchasing `StoreProduct` instead of `Package` (#1875) via NachoSoto (@NachoSoto)
* `ErrorUtils`: added test to verify that returned errors can be converted to `ErrorCode` (#1871) via NachoSoto (@NachoSoto)