feat: Lazy load panels

[bmingles]

Panels now lazy load the first time they are shown.

Can be tested using:

from deephaven import time_table

simple_ticking = time_table("PT2S")

simple_ticking2 = time_table("PT2S")

simple_ticking3 = time_table("PT2S")

• simple_ticking tab should load as usual
• Clicking simple_ticking or simple_ticking2 will show spinner the first time. Switching to another tab and back again should show what is already loaded without spinner
• Closing tabs and re-opening from PANELS should re-open tabs

resolves #52

[github-actions]

End-to-end Test Summary

Tests 📝	Passed ✅	Failed ❌	Skipped ⏭️	Pending ⏳	Other ❓	Flaky 🍂	Duration ⏱️
6	6	0	0	0	0	0	05:08:03

A ctrf plugin

Detailed Test Results

Name	Status	ms	Flaky 🍂
should default to the correct settings	passed ✅	2030
should return custom settings: Empty configs	passed ✅	235
should return custom settings: Populated configs	passed ✅	120
should be able to load VSCode	passed ✅	912
should only be visible when a supported file type is active: test.groovy	passed ✅	3036
should only be visible when a supported file type is active: test.py	passed ✅	1250

A ctrf plugin

Failed Test Summary

No failed tests ✨

Flaky Test Summary

No flaky tests detected. ✨