vector related fixes

[alex-s168]

• get rid of buffer.lm
• add vector unit test
• fix vector
• re-write to-string(U64) to use vectors

Checklist before requesting a review

• I have performed a self-review of my code
• If it is a new feature, I have added thorough tests.
• I agree to release these changes under the terms of the permissive MIT license (1).

1. https://github.com/andrew-johnson-4/lambda-mountain/blob/main/LICENSE

[andrew-johnson-4]

!!! get rid of buffer.lm

good job.

[andrew-johnson-4]

All the specialized Buffer instead of generic Vector<U8> specialized code is almost gone from the compiler finally. I think there are only one or two more specialized list-like types.