Add support for offline storage of errors to Raygun4Net Core

[xenolightning]

Add offline storage of crash reports to Raygun4Net

• This adds a new class OfflineStoreBase
• This class can be extended to support any sort of storage of errors, and any custom logic
• We have 2 default store implementations, FileSystem and Local App Data
• New interface IBackgroundSendStrategy which is used to determine how often the store should attempt to send it's errors
• By default there is a timer based strategy, which uses a background timer to initiate a check at certain intervals

All these classes are designed to be able to be updated/changed by users if they need specific functionality

MAUI will have it's own store implementation

This is an early implementation to allow for early feedback and suggestions

It is intended that the storage is treated as a singleton. There are default implementations in the net core project, but for other providers such as MAUI there should be another implementation.

There is also a singleton background sender, which has an internal timer.

Due to the way RaygunClientBase isn't exactly a singleton, we need to loosely couple the actual send method using a delegate (gross)

[xenolightning]

@phillip-haydon this is mostly ready for review.

Can review the approach, and the linkage to the client for now

There is a singleton background worker, and it is wired up to a cache - which should also be a singleton.

The clients (not a singleton yet) can then use the offline store to put failed crash reports, to be picked up by the background worker at a later date.

If it fails to send, then it does not remove the cached error from the disk

[PanosNB]

Lot's of good work! Some questions on my end

[xenolightning]

Tagged phill to review the public api surface in specific areas

[phillip-haydon]

Only 1 comment..

[PanosNB]

All good! A couple of non-blocking comments

[phillip-haydon]

😠

[PanosNB]

Looks good to me!