Refactor: Make swift concurrency core implementation - FileDownloadable

[Aldo10012]

What's the reason for this PR?

Inside of the different request performing class, we support:

• async/await & AsyncStream (Swift Concurrency)
• completion handlers
• publishers (Combine)

To prevent writing duplicate code, the completion handler method was used as the CORE implementation, and Swift concurrency and combine methods are wrappers of the completion handler method.

Apple recommends that any new async code should be written in Swift Concurrency.

Follow up to:

• Refactor: Make swift concurrency core implementation - RequestPerformable #89

What's new?

This PR focuses on FileDownloadable. Other classes will be refactored in follow up PRs.

1. Make swift concurrency method the core implementation handling networking logic,
2. Make non swift-concurrency methods be wrapper methods.
3. Replace .downloadFileTask(...) return type from URLSessionDownloadTask to CancellableRequest

[codecov]

Codecov Report

❌ Patch coverage is 90.13158% with 15 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
.../EZNetworking/Util/Downloader/FileDownloader.swift	90.56%	5 Missing ⚠️
...formers/Mocks/MockRequestPerformerURLSession.swift	0.00%	2 Missing ⚠️
...ataUploader/Mocks/MockDataUploaderURLSession.swift	0.00%	2 Missing ⚠️
...ileUploader/Mocks/MockFileUploaderURLSession.swift	0.00%	2 Missing ⚠️
...Util/WebSocket/Mocks/MockWebSockerURLSession.swift	0.00%	2 Missing ⚠️
...ZNetworking/Util/Performers/RequestPerformer.swift	66.66%	1 Missing ⚠️
...ownloader/Mocks/MockFileDownloaderURLSession.swift	85.71%	1 Missing ⚠️

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