refactor(node): remove more expect calls in node.rs

[dan-da]

Addresses #247 (more to come)

When combined with #265, all except 2 unwrap/expect are removed from node.rs. The remaining 2 expect occurrences are Mutex::lock().expect(), which I consider acceptable (necessary evil) for now.

This PR endeavors to keep the overall logic the same, except that:

• add_block() failure(s) results in logged error rather than panic. (logged by main init and tasks: do_handle_mined_block and receive_message)
• handle_request() failures due to inconsistent block data results in logged error rather than panic. (logged by main task receive_request)
• handle_message() failure due to "bad magic" (wrong network) results in logged error rather than silently failing. (logged by main task receive_message).
• get_time() is replaced by try_get_time() in a few places, and failure is logged in main() and main task loop is paused with explanatory log message (trying again each time it wakes up)

node.rs

• add 4 variants to NodeError
• return Result<_, NodeError> from add_block() and related Node methods.
• replace some expect calls with NodeError::Inconsistency
• return NodeError::BadMagic error from ::handle_message()
• log error in Node::main if receive_message task fails
• log error in Node::main if receive_request task fails
• log error in Node::main if handle_mined_block task fails
• log error and pause tasks in Node::main if try_get_time() fails
• replace get_time() with try_get_time() where possible

persistence.rs

• return Result from closure arg to BlockStorage::read_blocks()

util.rs

• change EpochError visibility: pub(crate) --> pub

[racs4]

Very good job. The code looks perfect

all except 2 unwrap/expect are removed from node.rs

But I think there are still more places causing panic like the HashMap accesses made in add_block, that are of the type: self.map[hash]

[dan-da]

But I think there are still more places causing panic like the HashMap accesses made in add_block, that are of the type: self.map[hash]

yeah, I've just been going after unwrap/expect until now. I intend to make another pass for array index stuff.

[racs4]

I intend to make another pass for array index stuff.

That would be in another PR, correct?

[dan-da]

yes, in another PR I mean. trying to keep them as small/focused as I can so easier to review.