[ON-HOLD] feat: Add some filetype guessing capabilities

[tmathern]

• Add some very basic filetype guessing capabilities to handle files that are extensionless but the recommendation for usage would be to use files with extensions. So there is no doubt about the filetype.

[gpeacock]

This is a great example of why I want most of the functionality tests in Rust instead of repeating them in every language. The appropriate level of testing in python should just be to validate that a file without an extension can be processed. The rest of the tests should be handled in Rust so that we don't need to duplicate them, and all the test files everywhere. Large test files slow down builds.
I'd prefer most of these test files to only live in one place. We may want to create a separate repo for them if they really need to be shared like this.

[tmathern]

This is a great example of why I want most of the functionality tests in Rust instead of repeating them in every language. The appropriate level of testing in python should just be to validate that a file without an extension can be processed. The rest of the tests should be handled in Rust so that we don't need to duplicate them, and all the test files everywhere. Large test files slow down builds. I'd prefer most of these test files to only live in one place. We may want to create a separate repo for them if they really need to be shared like this.

So hmmm, how do we proceed? Do you want me to remove the test files (and related tests for the mimetype guessing, then - aka the whole TestHelpers class currently)? As I added 3 tests that cover extensionless files.
Noting that this becomes obsolete once that code has been pulled down there.

[tmathern]

Let's put a pin in that for now - if the guessing moves down soon to the c2pa-rs Rust code SDK, we can heavily simplify that (by just adding the tests to verify the functionality).