fix(nano): improve error handling

[glevco]

Motivation

Nano error handling relies on catching NCFail after nano execution and making the transaction fail. Any other exceptions bubble up and will crash the full node. Also, any exception that inherits from Exception and is thrown by user code, is converted to NCFail.

The old PR #1321 tried to address error handling but it was unnecessarily complex. This PR replaces #1321 by extracting only the necessary changes from it, most notably, it ensures all nano-related exceptions do inherit from NCFail. This is necessary because any exception that is thrown by the runner before user code is called, must inherit from NCFail to fail the transaction instead of crashing the full node, because such exception will not be converted.

Acceptance Criteria

• Refactor nano exceptions, removing NCError and making ALL exceptions inherit from NCFail.
• Move the user code try-except block closer to the actual call to user code, that is, from the runner to the metered_exec.

Checklist

• If you are requesting a merge into master, confirm this code is production-ready and can be included in future releases as soon as it gets merged