Add control for mining process before starting mining

[Neylix]

Description

Add a control before starting mining a transaction, to check if the transaction is not already in mining process

Fixes #459

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Added latency in mining process, and tryed to send 2 times the same request. It blocked well the second transaction

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules