Add UUID v7 support (and v6/v8)

[sshaheerkhann]

Closes #204

Summary

Adds UUID version 6, 7, and 8 type support to pydantic-extra-types.

What's included

• UUID6, UUID7, UUID8 — Annotated uuid.UUID types that validate the UUID version
• uuid7() — Generation function using uuid.uuid7() on Python 3.14+ and uuid-utils on older versions
• uuid7_to_datetime() — Extracts the embedded UTC timestamp from a UUID v7
• Optional uuid-utils dependency for Python < 3.14
• 23 new tests covering validation, serialization, generation, and timestamp extraction

Usage

from pydantic import BaseModel
from pydantic_extra_types.uuid_types import UUID7, uuid7, uuid7_to_datetime

class Document(BaseModel):
id: UUID7

doc = Document(id='018f0e8c-7a6a-7b1c-a3e4-fdf3e0ef7a4a')
new_id = uuid7()
dt = uuid7_to_datetime(doc.id)