Forman/v0.3.0 py paths segm simplification

[forman]

Summary

• Removed Python-only Property and Index path segment classes.
• Aligned Python parsed paths with TypeScript: paths are now primitive segments, e.g. ("items", 0, "label").
• Updated Python store internals, path tests, store tests, README, and changelog for the new path model.
• Simplified TS path type aliases so PathInput mirrors the Python shape more closely.

Notes

• Root array entries are addressed as "[0]" or (0,), not bare 0.
• bool is explicitly rejected as a Python path index.

Checklists

Python package

• pixi run format
• pixi run lint
• pixi run mypy
• pixi run tests
• Updated remotestate-py/CHANGES.md

TypeScript library

• npm run format
• npm run checks
• npm run tests
• npm run build
• Updated remotestate-ts/CHANGES.md

Demo app

• npm run checks
• npm run build
• Updated remotestate-demo/CHANGES.md