chore: Prep for v0.2.0 release (#321)

Doc updates to prepare for `v0.2.0` release. Merge this just before
publishing on PyPI.

feat: Add `delete_nested_attribute` in torch_brain.data` (#299)

- Adds `Data.delete_nested_attribute(path)` symmetric with the existing
`get`/`set`/`has` methods
- Deletion guards live on `__delattr__` of each class (`Data`,
`ArrayDict`, `IrregularTimeSeries`, `Interval`), not on the API method,
so protection applies regardless of how `delattr` is called:
- `IrregularTimeSeries.timestamps` and `Interval.start`/`end` always
blocked
- Other registered timekeys can be deleted and are auto-deregistered
from `_timekeys`
- `_resolve_to_parent` helper refactors shared path-walking logic from
`get`/`set`/`delete`
- Fixes latent bug: `LazyIrregularTimeSeries` was not explicitly
imported in `data.py`

release v0.1.2

Updates CHANGELOG

Merge branch 'main' into vinam/v0.1.1

V0.1.0 (#92)

* update README.md

* rename pypi dist package

* add discord

* update docs