Refactor mintscript tests - put the expected output directly into the code

[ImplOfAnImpl]

The current tests in mintscript are rather hard to maintain because the expected values are in separate files with not very descriptive names.
In this PR I've put the expected values directly into the code and removed the files.

The tests can still be improved though (e.g. it'd be better if the expected values were Rust objects instead of their string representations), I've left a TODO about it.

Edit:

1. there was also a test failure in input_commitments::order_fill test in the chainstate test suite, due to a low initial amount being generated (not enough to do 2 fills), I fixed it here by increasing the amounts and also did the same in another similar test.
2. there was also another clippy 1.88 failure due to a large enum variant.