Motivation:

While working to add more test coverage with `RESPTranslator`, it was made apparent that a `.bulkString(.none)` is impossible to create directly with the `RESPValue` initializers, even though it is a reasonable possibility.

Additionally, forcing all integer types to have to be stored in an `Int` is unnecessarily restrictive.

Modifications:

- Change `RESPValue.init(bulk:)` initializers to accept `Optional` instances
- Change `RESPValue.init(bulk:)` for `Int` initializer to be generic on `FixedWidthInteger`

Result:

Converting types to and from `RESPValue` should be more bi-directional and seamless.