Feat/#1752 fix witness generation - adding testing

[KimiWu123]

Description

closed #1752

• Adding different numbers of txs to test different trie status (e.g. one leaf only, one ext. , one branch and one leaf ...etc)
• Fixing GetProof (if input is an ext node, it always assign first child of the root ext. node, st.children[0])
• Fixing getNodeFromBranchRLP (if input is an leaf, it could throw an exception)
• Refactoring getNodeFromBranchRLP

Issue Link

1752

Type of change

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

[KimiWu123]

Hey @miha-stopar , I think I fixed everything. Could you please give it a quick review again.