[Feature]: Return Result instead of Panicking in Internal Functions

[0xNeshi]

What is the feature you would like to see?

Many functions internal to motsu panic in certain conditions, causing error handling to be more challenging.
One example of this is that error messages get too long, see #35

The solution is to return Result instead of panicking. That way we make it clear to our future selves which functions can error out, thus avoiding any surprises when invoking them. An extension of this is that we also avoid the need to have to read the func docs to know that it can panic.

Prompted by #31 (comment)

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