fix: .length on chained method call results returns correct value

[cs01]

Summary

• [1,2,3,4,5].filter(x => x > 3).length was returning 5 (original array length) instead of 2
• Root cause: handleLengthProperty had no handler for method_call/call expression types — fell through to getStringLength which treated the array pointer as a string
• Added type-aware dispatch for method call results: checks getVariableType on the generated result and routes to the correct array/string length getter

Test plan

• New fixture arrays/filter-chain-length.ts — filter().length on both number[] and string[]
• All tests pass (619 total)
• Self-hosting verification passes

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