fix(optimiser): Prevent invalid time range

[sevensxyt]

Context

On the optimiser page, time options for the dropdown lists are not filtered. This allows invalid time ranges to be selected, where the start time is after the end time, as shown below:

Start time 18:00 is after end time 14:00

Implementation

• I've abstracted the time ranges into constants, and stored the start/end times for class/lunch as state
• When start time is selected, we filter out end times to include options that are after start time
• This prevents users from selecting an invalid range where start time is after end time, as shown below:

Other Information

I've also added tests for the utility functions added

[vercel]

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nusmods-export	Ready	Preview	Comment	Aug 18, 2025 0:06am
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[codecov]

Codecov Report

❌ Patch coverage is 23.07692% with 20 lines in your changes missing coverage. Please review.
✅ Project coverage is 52.91%. Comparing base (988c6fd) to head (94ea529).
⚠️ Report is 137 commits behind head on master.

Files with missing lines	Patch %	Lines
website/src/views/optimiser/OptimiserForm.tsx	0.00%	20 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4113      +/-   ##
==========================================
- Coverage   54.52%   52.91%   -1.62%     
==========================================
  Files         274      289      +15     
  Lines        6076     6696     +620     
  Branches     1455     1633     +178     
==========================================
+ Hits         3313     3543     +230     
- Misses       2763     3153     +390     

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[leslieyip02]

Hi @sevensxyt, thanks for the PR. I'm currently working on a refactor of the optimiser component in #4094, and it also modifies the time select. I'll update you again when those changes are ready.

[leslieyip02]

Hi @sevensxyt, #4094 has been merged.

Let me know if you are still interested in working on this. Thanks for your patience and sorry for the delay!