VER: Release 0.25.0

[threecgreen]

Breaking changes

• Renamed VersionUpgradePolicy::Upgrade to UpgradeToV2 in preparation for a future
  DBN version 3

Enhancements

• Added v1 and v2 modules to allow unambiguously referring to the record types for
  a given DBN version regardless of whether the record type has changed. Previously
  versioned aliases only existed for record types that have changed between DBN versions
  • Added identical namespaces to databento_dbn Python package
• Changed dataset() method on MetadataBuilder to accept an impl ToString so now
  Dataset and &str can be passed directly
• Added type aliases for TBBOMsg, BBO1SMsg, BBO1MMsg, TCBBOMsg, CBBO1SMsg,
  CBBO1MMsg in Python

Deprecations

• Deprecated dataset module. The top-level Dataset enum and its const as_str()
  method provide the same functionality for all datasets. This module will be removed in
  a future version

[nmacholl]

LGTM 🚀