fix: assertion analyzers missing rules for common mistakes

[thomhurst]

Description

The assertion analyzers check for missing await, constants, dynamic usage, and mixed And/Or operators. Missing rules for common mistakes:

1. GenerateAssertionAnalyzer doesn't catch Task (non-generic) return types — should require Task<bool> or Task<AssertionResult>
2. No sync-blocking detection — .Result or .Wait() on assertion expressions
3. No assertion chain completeness — And without a following assertion
4. No assignment detection — using = instead of assertion in Assert.That()

Suggested Fix

Add new analyzer rules for each case above, with appropriate diagnostic IDs and fix suggestions.