feat(snapshot): add document symbols and folding support

[Gehbt]

Document symbol support

Folding range support

[Copilot]

Pull request overview

Adds VS Code language features (document symbols + folding ranges) for vitest-snapshot files in the extension, alongside a couple of small maintenance updates.

Changes:

• Introduce snapshot parsing utilities and wire up DocumentSymbolProvider + FoldingRangeProvider for vitest-snapshot.
• Fix typos in the logging API (openOutput, exists).
• Update Vitest e2e global setup typing and add a snapshot fixture file for testing/demo.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
test/e2e/utils/downloadSetup.ts	Updates Vitest globalSetup context typing used by e2e setup.
samples/basic/test/snap/fixture.test.ts.snap	Adds a .snap fixture used to exercise snapshot parsing/symbols/folding.
packages/extension/src/snapshot/tools.ts	Implements snapshot entry extraction + symbol-building helpers.
packages/extension/src/snapshot/foldingRangeProvider.ts	Provides folding ranges for each snapshot entry.
packages/extension/src/snapshot/documentSymbolProvider.ts	Provides Outline symbols grouped by snapshot “breadcrumb” segments.
packages/extension/src/log.ts	Fixes typos in the log API method/variable names.
packages/extension/src/extension.ts	Registers the new snapshot symbol and folding providers.

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