bump version to 0.1.6

[matt-phylum]

Overview

• with_subpath no longer bypasses subpath canonicalization.
• The subpath a/%2E%2E/b parses as a/b instead of resulting in ParseError::InvalidEscape (matches a PURL spec change made 2025-02-19)
• type validation ensures that the first character of the type is a letter, as required by the PURL spec (only applicable when using the string shapes)
• & characters in qualifier values are escaped to prevent pkg:generic/name?q=a%26b=c turning into pkg:generic/name?q=a&b=c

These changes should be safe. I'm expecting that some time soon PURL will make a breaking change to canonicalization (it's basically unavoidable because the spec wasn't clear and all the implementations interpreted it differently). This may be the last release in the 0.1.x line.

Checklist

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Issue

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