fix: Parsing of runGetMethod

And misc. fixes:
- Better usage of Cell.fromBocBase64 function
- Updated wallet address for TonJsonRpc tests

fix: correct signature length

crypto:
• sign function now returns a signature
• signVerify function now verifies using the provided signature
• safeSignVerify now uses signatures
• added doc comments for safeSign and safeSignVerify

Fix #1

Fully implemented TON Footstep 224 — Dart/Flutter library for TON Blo…

…ckchain!