test: fix optimization related tests

[jaeminy00]

This pull request updates the test suite for the optimization module to reflect a shift from using "ramp_rate" to "ramp_step_time" as the primary parameter for ramping behavior. The changes ensure that tests and parameter handling are consistent with this new approach and improve backward compatibility.

Test updates for ramp parameters:

• Replaced all usage of ramp_rate with ramp_step_time in tests for OptimizableRecipe, including parameter creation, assertions, and backward compatibility checks. [1] [2] [3] [4]

Test updates for search space construction:

• Updated search space tests to use add_ramp_step_time_range instead of add_ramp_rate_range, and changed assertions to expect ramp_step_time as a discrete parameter. [1] [2] [3]