How to consolidate At-Uri validation?

[zzstoatzz]

Note

wip, i will update this over time when possible 🙂

#451 adds the following regex into string_formats.py

AT_URI_RE = re.compile(
    r'^at://'  # Must start with at://
    r'('  # Authority group start
    # For DIDs: Only allowed chars are letters, numbers, period, hyphen, and percent
    r'did:[a-z]+:[a-zA-Z0-9.-]+'  # Notice removed underscore from allowed chars
    r'|'  # or
    # Handle: require 2+ segments, TLD can't start with digit
    r'[a-zA-Z0-9]([a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?'  # First segment
    r'(\.[a-zA-Z0-9]([a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*'  # Middle segments
    r'\.[a-zA-Z][a-zA-Z0-9-]*'  # TLD must start with letter
    r')'  # Authority group end
    r'(?:'  # Optional path group
    r'/[a-z][a-zA-Z0-9-]*(\.[a-z][a-zA-Z0-9-])+'  # NSID
    r'(?:/[A-Za-z0-9._:~-]+)?'  # Optional record key
    r')?$'
)

but it was unclear to me how exactly to square the new interop tests (sourced from here) with the current validation in packages/atproto_core/uri/uri.py:AtUri (which was probably me just not understanding something 🙂 )

see #451 (comment) for context

here are the upstream atproto docs I referenced

related to #478