Add DataUri type to web domain

[oborchers]

Summary

Add a DataUri type to the web domain for validating RFC 2397 data URIs (data:[<mediatype>][;base64],<data>). This fills a documented gap in Pydantic — AnyUrl explicitly does not support data: URIs (see pydantic#2157).

Proposed Type

DataUri (Pattern A — str subclass)

• Spec: RFC 2397 — The "data" URL scheme
• Domain: web/
• Format: data:[<mediatype>][;base64],<data>
• Parsed properties:
  • .media_type → str (e.g. "text/plain", "image/png", defaults to "text/plain;charset=US-ASCII" per RFC)
  • .is_base64 → bool
  • .data → str (the raw data portion after the comma)
• Usage: Common in web APIs, ML model serving (embedding images/audio), configuration files, email templates, and data pipelines. Pydantic's AnyUrl explicitly rejects data: URIs, making this a known ecosystem gap.
• Examples:
  • "data:,Hello%20World" (plain text, no mediatype)
  • "data:text/plain;base64,SGVsbG8gV29ybGQ=" (base64-encoded text)
  • "data:image/png;base64,iVBORw0KGgo..." (embedded image)
  • "data:application/json,{\"key\":\"value\"}" (inline JSON)

Verification

• Fills a documented Pydantic gap (pydantic#2157)
• Not in Pydantic core, pydantic-extra-types, or any known Pydantic-native library
• Regex/parsing only — no external service calls
• Follows Pattern A per ARCHITECTURE.md (str subclass with parsed properties)

Implementation

• File: src/pydantypes/web/data_uri.py
• Tests: tests/web/test_data_uri.py
• Export: Add to src/pydantypes/web/__init__.py