Function lookup costs missing

[ureeves]

While adding test infrastructure for cost tracking it was noticed that the current implementation doesn't track the costs of function lookup, whereas this is done in the interpreter. This can easily be observed in, for example, test_subtraction with --features=test-clarity-v1,test-cost-tracking.

thread 'words::arithmetic::tests::test_subtraction' panicked at clar2wasm/src/tools.rs:596:9:
assertion `left == right` failed
  left: LimitedCostTracker { total: ExecutionCost { write_length: 0, write_count: 0, read_length: 0, read_count: 0, runtime: 169 }, limit: ExecutionCost { write_length: 9223372036854775807, write_count: 9223372036854775807, read_length: 9223372036854775807, read_count: 9223372036854775807, runtime: 9223372036854775807 }, memory: 0, memory_limit: 100000000 }
 right: LimitedCostTracker { total: ExecutionCost { write_length: 0, write_count: 0, read_length: 0, read_count: 0, runtime: 185 }, limit: ExecutionCost { write_length: 9223372036854775807, write_count: 9223372036854775807, read_length: 9223372036854775807, read_count: 9223372036854775807, runtime: 9223372036854775807 }, memory: 0, memory_limit: 100000000 }