Some lambda schedules fail validation when num_windows < 5

[maxentile]

Migrating from this thread: #712 (comment)

Problem:

validate_lambda_schedule fails assertion that endpoints exactly == 0.0 or 1.0, for some lambda schedules generated with num_windows < 5 .

Extent:

Locally it looks like this is a problem with the methods that use linspace and concatenate:

• construct_absolute_lambda_schedule_solvent
• construct_absolute_lambda_schedule_complex
• construct_relative_lambda_schedule

but not with the method that uses interp

• construct_pre_optimized_absolute_lambda_schedule_solvent