Adds test for methods in vec, map and bytes (#840)

[Ray-Escobar]

What

Adds tests for the methods within the modules Vec, Map and Bytes.

Tests have been added for the following methods...

Bytes: is_empty, first, first_unchecked, last, last_unchecked, get, get_unchecked, remove, remove_unchecked, pop, pop_unchecked, insert, slice

Map: from_array, contains_key, is_empty, get, get_unchecked, remove, remove_unchecked

Vec: get, get_unchecked, remove, remove_unchecked

Why

These modules are the building blocks of soroban-sdk.

Extra

I refactored some tests names in Vec so that they are pre-pended with the word test. It seems the majority of the tests follow this convention, but I also stopped short in case the renaming is not necessary. I do find its useful as an easy way to search files i.e. if you want to look for tests simply use the query "find_" on all your files.

[Ray-Escobar]

On a side note, there are some println! statements in lines 1144 and line 1165 in the tests for bytes.rs. Should I go ahead and remove them?

[jayz22]

@Ray-Escobar thanks for the PR! I will take a look at the tests soon.
As for print statements, we normally don't have them (either active or commented out) in our code base, so I would suggest removing them.

[Ray-Escobar]

@jayz22 thanks! I am very open with feedback so be as critical as you need.

[leighmcculloch]

Thanks for adding tests!

If possible I'd like us to change how we assert the panics so that we're asserting on the specific function that we expect to panic. See inline comment.