fix(lint): resolve parsing errors and style violations from vitest migration

[Copilot]

Fixes lint errors introduced during the Jasmine to vitest migration that blocked CI builds.

Changes

Parsing Errors

• Removed malformed empty property syntax in mock objects from tree-selection.service.spec.ts and tree-selection.spec.ts
• Jasmine's createSpyObj('tree', ['']) with empty method array incorrectly migrated to invalid object literal syntax

Before (invalid):

mockTree = {
    : vi.fn().mockName("tree."),
    selection: IgxTreeSelectionType.BiState
};

After:

mockTree = {
    selection: IgxTreeSelectionType.BiState
};

Auto-fixable Style Violations

• Applied npm run lint --fix to resolve 117 brace-style violations across 47 test files

Impact

• Lint errors: 119 → 0
• Remaining warnings (148) are non-blocking and pre-existing

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