feat: allow ALTER TABLE to modify the skip_wal option dynamically

[JoeS51]

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Fixes this issue

What's changed and what's your intention?

This PR now allows the ALTER TABLE command to update skip_wal at runtime instead of only at table creation time. To support this operation safely, this PR separates WAL provider configuration from the runtime “skip WAL” toggle. Previously, Greptime used WalOptions::Noop to indicate that a region should skip WAL writes. This makes re-enabling WAL unsafe because the original provider information will be be discarded. (see discussion)

This PR introduces skip_wal as a new region option and uses it as the runtime signal for whether WAL writes should be skipped, while preserving the region’s provider specific wal_options. New regions created with skip_wal=true still keep real WAL provider metadata, so WAL can later be re-enabled safely.

For backwards compatibility, legacy regions that already persist WalOptions::Noop are still supported as "skip wal" regions, but attempting to re-enable WAL for those legacy regions now fails explicitly because the original provider information is unavailable (please let me know if there is a better solution for this).

PR Checklist

Please convert it to a draft if some of the following conditions are not met.

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.
• This PR requires documentation updates.
• API changes are backward compatible.
• Schema or data changes are backward compatible.

[gemini-code-assist]

Code Review

This pull request introduces a skip_wal option for regions and tables, allowing the Write-Ahead Log to be bypassed for specific operations. The changes include updates to region and table options, modifications to the write and close paths to respect the new flag, and validation to prevent enabling WAL on legacy regions created with a no-op provider. Review feedback suggests improving maintainability by refactoring the WAL-skipping check into a centralized helper method in RegionOptions and simplifying the validation logic in the alter handler for better idiomaticity.