[SL-3596] [Feature] Migrate to msgspec

[plypaul]

Is this your first time submitting a feature request?

• I have read the expectations for open source contributors
• I have searched the existing issues, and I could not find an existing issue for this feature
• I am requesting a straightforward extension of existing metricflow functionality, rather than a Big Idea better suited to a discussion

Describe the feature

Python-native dataclasses are widely used in the codebase, and they are not the most efficient in a few areas (e.g. object initialization and hash computation). Initial benchmarks on msgspec are promising, and once larger performance improvement changes are in place, we should try out msgspec. Another advantage of msgspec is that it can replace some custom methods / classes for serialization.

Describe alternatives you've considered

Pydantic

Who will this benefit?

All users.

Are you interested in contributing this feature?

No response

Anything else?

No response

_SL-3596