Enforce Leading and Trailing double quote in ByteMachine

## What is your idea?
In actual usage of Ruler, ByteMachine stores string values always with a beginning and ending double quote. However, ByteMachine is capable of storing string values that begin and end with any character. This unnecessary flexibility leads to more complexity and special cases, for example, to support a leading or trailing wildcard character for wildcard patterns. We can simplify the code and remove some special cases by updating ByteMachine to either enforce the leading/trailing double quotes itself, or to be the component that adds these double quotes.

## Would you be willing to make the change?
Maybe.

## Additional context
Discussion arose during: https://github.com/aws/event-ruler/pull/18

Start by reading the ByteMachine implementation and the discussion from pull request 18. Determine whether ByteMachine should enforce or add leading and trailing double quotes, then inspect the surrounding wildcard-handling behavior. Done means the chosen invariant removes the described special cases without breaking string matching.

Written by the indexing model from the issue text.