Added FilecachedInputOutputStream

[brototyp]

This PR adds a FilecachedInputOutputStreamSpec. This is a Stream that can written to and read from. This will be used, so when data is received from the server, we can pass the data one layer up while having a file everything is written to.

[brototyp-bot]

	1 Error
:no_entry_sign:	Please include a CHANGELOG entry to credit yourself! You can find it at /CHANGELOG.md.

	3 Warnings
:warning:	Are there any changes that should be explained in the README.md?
:warning:	Cauli/Data structures/Record.swift#L52 - Top-level declarations should specify Access Control Level keywords explicitly.
:warning:	Cauli/Data structures/Record.swift#L54 - Top-level declarations should specify Access Control Level keywords explicitly.

Example CHANGELOG entry

* **feature/improvement/bugfix** Added FilecachedInputOutputStream  
  [#issue_number](https://github.com/cauliframework/cauli/issues/issue_number) by @brototyp  

Trivial PR?

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