Wring out starline parsing

[CyberiaResurrection]

Tighten up starline parsing according to the following property:

Given a string conforming to the ParseStarInput.starline regex, it either:

1. Is cleanly rejected by parse_line_into_star, or;
2. Is cleanly accepted and parsed by parse_line_into_star into a Star object.

Given 2, above, it should then be output to a string representation, cleanly re-parsed by parse_line_into_star, and then output to the same string representation.
IOW, re-parsing a Star object should be idempotent in the string representation.

Given that hypothesis is already hooked up and running clean, the next step was to hook up hypofuzz - a hypothesis-powered fuzzer.
I hooked up hypofuzz in another branch and probably won't be pushing the hookup up for review, as it brings in a whole lot of packages to view the fuzzing results that aren't relevant to PyRoute.

I then started a cycle of "run hypofuzz until property is violated - fix violation - repeat" until it ran cleanly overnight (approx 11 h 45 min, and ~103k inputs, all without triggering a new path, let alone finding a property violation).

Yes, it is very unlikely that the strings added as examples will even turn up in production - but now, those strings (and strings like them) are far less likely to cause any sort of parsing issue.