Support development without access to EP-internal infrastructure

[NMertsch]

Summary

Add a static Pretix mock service via scripts/pretix-mock.py.

Relates to #220

Rationale

The bot requires access to a Pretix instance, and we (obviously) don't provide public access to our ticketing system.
This is a high barrier for contributors.

Details

This PR allows contributors to run use a local Pretix mock instance:

• Run: python scripts/pretix-mock.py --port 8080
• Configuration: registration.pretix_base_url = "http://localhost:8080"

The mock instance contains the following orders (names are common placeholder names):

Order 'AAAAA' (paid)

• Business Combined Ticket for 'Jane Doe'
• Business Tutorial Ticket for 'John Doe'
• Childcare

Order 'BBB22' (paid)

• Volunteer Ticket for 'Minta János'
• Speaker Ticket for 'Minta Kata'
• T-Shirt

Order 'CCC33' (paid)

• Personal Remote Ticket for 'Martina Mustermann'

Order 'DDDD44' (paid)

• Sponsor Ticket for 'Seán Ó Rudaí'
• T-Shirt

Order 'EEE55' (payment pending)

• Personal Late Conference Ticket for 'Numerius Negidius'

Other changes

• Make pre-commit hooks independent from uv
• Silence superfluous Discord.py warning (PyNaCl warning issued, even though VoiceClient not being used Rapptz/discord.py#1719 (comment))