chore(deps): update oxc (major)

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
miette	workspace.dependencies	major	2.7.0 → 3.0.0
oxc_sourcemap	workspace.dependencies	major	7.0.0 → 8.0.0

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[Brooooooklyn]

@claude[agent] fix oxc upgrade breaking changes

[Brooooooklyn]

@claude[agent] fix oxc upgrade breaking changes

[Brooooooklyn]

@copilot fix oxc upgrade breaking changes

[Copilot]

@copilot fix oxc upgrade breaking changes

Fixed in commit fix: update severity field access for oxc-miette v3 API change.

In oxc-miette v3, severity changed from a trait method returning Option<Severity> to a direct struct field of type Severity on OxcDiagnosticInner. The default value is Severity::Error, so the old is_none() guard (which treated diagnostics with no severity as errors) is now handled implicitly by the field's default — behavior is preserved.