Support filtering on table calculations #21

Use case

Users define table calculations in SDK queries and need to filter results based on those calculated values. The API already supports table calculation filters via filters.tableCalculations, but the SDK has no way to reference table calculations in .filter() calls.

Root cause

The SDK's filter system is built exclusively around Dimension objects:

• DimensionFilter in filter.py validates that field is a Dimension instance
• CompositeFilter.to_dict() serializes all filters under the "dimensions" key
• There is no TableCalculationFilter class or "tableCalculations" serialization path

Proposed solution

Add a filter type for table calculations that serializes under filters.tableCalculations in the API payload, similar to how DimensionFilter serializes under filters.dimensions.