Update fable, fix backing fields

[caroott]

This PR updates DynamicObj for Fable 5.1.0 and fixes JS/Python dynamic property handling.

Dynamic members are now stored and enumerated through the internal Properties dictionary on Fable targets, so compiler-generated backing fields no longer leak through GetProperties(false). This removes the previous native JS/Python attribute behavior for dynamic members.

Changes

• Update Fable tooling/runtime test dependencies to 5.1.0
• Fix leaked backing fields in JS/Python dynamic member enumeration
• Fix Python ResizeArray deep-copy handling
• Make Python native == and hash() match DynamicObj structural equality/hash

[HLWeil]

Tests fail currently, I guess because a missing uv setup (maybe requirement resolving is missing). Could you check this, @caroott?

[caroott]

Tests fail currently, I guess because a missing uv setup (maybe requirement resolving is missing). Could you check this, @caroott?

Fable 5 changed Python output to import fable_library as an installed Python package, while older Fable output bundled it under fable_modules. CI created an empty .venv but never installed the dependencies from pyproject.toml, so Python could not find fable_library.

[HLWeil]

lgtm, thanks!