Path Successors [✨ surprises ✨]

[sgwilym]

Last week I naïvely thought: "let's quickly port the willow-utils path successor functions and get that out of the way". Things did not work out that way!

TL;DR: All path successor implementations up to this point are wrong, and we were only able to find out how using fuzz testing. willow-util's implementations need to be fixed, as it may be generating the wrong ranges for areas.

SubspaceId

• Added successor method.

PathComponent trait

• Added new_with_tail method
• Added empty method
• Added try_append_zero_byte method
• Added set_byte method
• Added try_increment_fixed_width method
• Added prefix_successor method

Path trait

• The iterator returned by the components method must implement ExactSizeIterator and DoubleEndedIterator
• Added component_count method
• Added is_empty method
• Fixed a bug is_prefix_of
• Added successor method
• Added successor_of_prefix method
• Added explicit implementations of Ord, PartialOrd

Testing

• Implemented Arbitrary for PathComponentBox
• Implemented Arbitrary for PathRc
• Added fuzz tests for Path::successor
• Added fuzz tests for Path::successor_of_prefix

[sgwilym]

@Frando you may want to check this against your own implementation for path successors.