Mint improve

[FabijanC]

Usage related changes

• Change tx_hash from mint response from int to hex string.
• Document lite minting.
• Add input validation for minting.

Development related changes

• Improve testing
• Add invalid input tests
• I reused old code for input validation, but had to slightly modify timestamp tests because of that (Time -> time)
• Replace single with double qoutes

Checklist:

• No linter errors
• Performed a self-review of the code
• Rebased to the last commit of the target branch (or merged it into my branch)
• Documented the changes
• Updated the tests
• All tests are passing

[tabaktoni]

🎉 Great job

• Do you think it will be good to export extract_positive & extract_hex_string to util.py same as custom_int formater/validator? Or place it at the top of the file before all routes?