Add more unit tests, improve test coverage

[motorina0]

Check paths that are not covered by the current unit tests and cover them.
Each new test covers a line/branch that was previously not covered/partially covered.

• bufferutils.ts
• ecpair
• script
• address
• types
  • BIP32Path - is this type still being used?
• embed
• p2sh
• p2wpkh

Before

=============================== Coverage summary ===============================
Statements   : 94.23% ( 2662/2825 )
Branches     : 91.74% ( 1611/1756 )
Functions    : 92.11% ( 420/456 )
Lines        : 95.93% ( 2451/2555 )
================================================================================

After

=============================== Coverage summary ===============================
Statements   : 94.8% ( 2678/2825 )
Branches     : 92.82% ( 1630/1756 )
Functions    : 93.2% ( 425/456 )
Lines        : 96.48% ( 2465/2555 )
===========================
=====================================================

[junderw]

Awesome! Thanks for the help!