The parser is not robust to whitespace

[MarquessV]

The parser considers 4 spaces as an indentation token, which means that 8 spaces should be considered 2 indentations. The parser is "flexible" in that it allows for extra spaces after the initial 4, but that has less precedence than recognizing an additional indentation, so 4-7 spaces becomes the valid range for a single indentation. This doesn't necessarily seem incorrect to me, but it is brittle, and not really made clear to the user.

Since quil-rs serializes program to Quil using tabs for whitespace, and many editors and terminals default to rendering 8 spaces for tabs, this leads to a surprising error when attempting to roundtrip a serialized program copied from one's editor or terminal.

Ideas:

• Allow configuration of whitespace when serializing a program. I can see this as an enum with a method that returns the desired whitespace. The serialization routine would then inject that whitespace instead of hardcoding '\t'
• Implement Python-esque handling of whitespace, where indentation must be consistent within a block, but the composition of said whitespace can vary.

[MarquessV]

Capturing additional feedback from team discussion:

• Whatever solution should be consistent with the Quil spec.
• The Quil spec may give us some leeway here. For example, Quil may not allow for nested blocks which means we could allow for irregular indentation by making 1 or many indentations equivalent to 1.