Environment Variables Suck

[thirtytwobits]

Many many reasons why but here are two things that need to be fixed:

1. Always recheck and rebuild the database when environment variables change. For example, I just wasted 15 minutes trying to figure out why pycyphal was trying to connect to UDP only to discover that my previous value UAVCANUDPIFACE was somehow part of the db. Once I deleted this and restarted my new environment variables were found.
2. Always accept "CYPHAL" where "UAVCAN" is currently required. It's really hard to remember which of the environment variables are UAVCAN and which are CYPHAL. Either should be accepted but CYPHAL should be documented.

[pavel-kirienko]

1. We can make it so that environment variables override all entries in the database during initialization, like the following but executed for all records in the db during construction:

   https://github.com/OpenCyphal/pycyphal/blob/01b9a9b57143bc916bfa2fa26102a787b4e558e9/pycyphal/application/register/_registry.py#L256-L261

2. This is outside of the scope of PyCyphal because the names come from https://github.com/OpenCyphal/public_regulated_data_types/blob/935973babe11755d8070e67452b3508b4b6833e2/uavcan/register/384.Access.1.0.dsdl#L80