Get the max_expected_time_per_block using the /genesis endpoint

[seanchen1991]

Background

We should take care of this TODO to get the max_expected_time_per_block using the /genesis endpoint in the src_max_block_time and dst_max_block_time functions.

Tasks

• Refactor src_max_block_time and dst_max_block_time to use the max_expected_time_per_block field fetched from the /genesis endpoint

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