Move osm-fieldwork core functionality to FMTM as workspace package

[spwoodcock]

Is your feature request related to a problem? Please describe.

• osm-fieldwork has our ODK API wrappers, plus XLSForm manipulation.
• Many API methods could be replaced with pyodk.
• Some are unique and we need to keep them, particularly the Async stuff.
• However managing a separate package that is so tied to FMTM has complications: continual need for new releases.
• We also want the package to remain available standalone for other users.

Describe the solution you'd like

• Create a uv workspace for osm-fieldwork in FMTM - manage in a monorepo.
• Still keep publishing of osm-fieldwork to pypi.
• I will be easier to mount and test functionality in FMTM.
• It also simplifies tests that rely on the full ODK stack.

Additional context

• This should be the best of both approaches.