Add utility `postConditionToHex`

[aryzing]

Problem

In the wake of the increasingly adopted WebBTC standard, and from how the [Integration of WebBTC Request Standard for Stacks Wallets SIP](Integration of WebBTC Request Standard for Stacks Wallets) is evolving, it would be helpful to have hex conversion helpers for all values recommended by the SIP to be used as hex,

• [done] Clarity values (covered by cvToHex)
• Post Conditions
• Transactions

Although user can 2-step this process by first serializing to bytes and then converting to hex, having a helper would make for a nicer DX.

Solution

Similar to the cvToHex helper, it would be helpful to have postConditionToHex() and txToHex() helpers.

[janniks]

Good point, thanks! There might exist some helpers, but I'll add aliases or build out the missing functions.