Cleanup and add validation to new adaptive saving strategy

[dlqqq]

Description

• Implements feedback on PR Refactor OutputsManager to align with default Jupyter behavior #163.
• Removes mostly unused _last_save_duration and poll_interval attributes.
• Adds validation for the new YRoomFileAPI.min_poll_interval and YRoomFileAPI.poll_interval_multiplier traits.
• Fixes CI failure on main after Refactor OutputsManager to align with default Jupyter behavior #163 was merged.
• Adds ui-tests/yarn.lock.

I verified that these changes does not break the current experience & correctly prevents users from configuring trait values <=0.

[dlqqq]

CI failure is not related, but it is happening on main as well.

Issue is reproducible by running cd ui-tests/ && jlpm. Looking into this now. This is the relevant error:

Resolution step
  ➤ YN0001: │ Error: vega-util@npm:^1.17.4: No candidates found
      at ge (/opt/hostedtoolcache/Python/3.12.11/x64/lib/python3.12/site-packages/jupyterlab/staging/yarn.js:439:7784)
      at process.processTicksAndRejections (node:internal/process/task_queues:95:5)

[dlqqq]

Weird, for some reason cd ui-tests/ && jlpm is trying to pull in patch releases of vega subpackages that do not exist. For each package raising an error, the requested patch release is 1 too high. Presumably this is an upstream bug in vega.

I've added these resolutions which decrease the patch version by 1 on every package raising an error on jlpm install:

  "resolutions": {
    "vega-util": "^1.17.3",
    "vega-dataflow": "^5.7.7",
    "vega-selections": "5.6.0",
    "vega-scale": "^7.4.2",
    "vega-scenegraph": "^4.13.1",
    "vega-time": "^2.1.3"
  }

To future devs: feel free to remove these resolutions if cd ui-tests/ && jlpm passes without these resolutions.

[3coins]

Looks good!

Verified that notebook behavior is intact with this change.