Update Solid 2.0 documentation for initial values

[titoBouzout]

Summary

Add docs about removal of @once and provides a migration path with alternative solutions.

Notes: needs from ryansolid/dom-expressions#523 to be merged

[changeset-bot]

⚠️ No Changeset found

Latest commit: 867d586

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[codspeed-hq]

Merging this PR will not alter performance

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

⚡ 1 improved benchmark
❌ 1 regressed benchmark
✅ 116 untouched benchmarks

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
⚡	omit	215.7 µs	202.3 µs	+6.65%
❌	color-picker: 14 colors (renderToString)	1.5 ms	1.6 ms	-7.38%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing titoBouzout:patch-4 (867d586) with next (4fb7218)}