Added a prerelease version to load_schema_version

[VisLab]

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[Copilot]

Pull request overview

This PR introduces support for loading HED schemas from a prerelease directory by adding a check_prerelease parameter to load_schema_version, updating cache path resolution accordingly, and adding basic tests/documentation updates around the new parameter.

Changes:

• Add check_prerelease parameter plumbing to load_schema_version and internal schema-loading helpers.
• Update hed_cache.get_hed_version_path to prefer regular schema files and fall back to prerelease paths when enabled.
• Add unit tests for check_prerelease parameter acceptance/backward compatibility; refresh docs landing page text.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
hed/schema/hed_schema_io.py	Adds check_prerelease parameter and threads it through schema loading calls.
hed/schema/hed_cache.py	Adjusts schema path selection to check regular files first, then prerelease when requested.
tests/schema/test_hed_schema_io.py	Adds tests covering parameter presence/defaults and ensuring regular schemas still load when enabled.
docs/index.rst	Updates documentation intro/section headings (includes a typo to fix).

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[Copilot]

Typo in section title: "Pythn HEDTools features" should be "Python HEDTools features".

Suggested change

	Pythn HEDTools features
	Python HEDTools features