fix: cast grading policy corretly as numbers

[nsprenkle]

Description

Fixes a typing issue in grading policies causing breakages on the progress page.

Jira - https://2u-internal.atlassian.net/browse/CR-8030

Supporting information

Some courses were running into the error below which was a result of a grading policy using strings instead of numbers for their values.

  File "/edx/app/edxapp/edx-platform/lms/djangoapps/course_home_api/progress/api.py", line 56, in with_placeholders
    scores=[0] * num_total,
           ~~~~^~~~~~~~~~~
TypeError: can't multiply sequence by non-int of type 'str'

This correctly casts numeric values in grading policies to numbers, allowing those mathematical operations to succeed, rather than fail.

Testing instructions

1. Import a course with grading policies represented with strings rather than numbers.
2. Load the progress page, verify breakage.
3. Load new changes.
4. Reload progress page, verify working.

Unit tests also updated.

Deadline

ASAP - fix for a C2 bug

[Copilot]

Pull request overview

Fixes progress page breakages when course grading policies contain numeric values encoded as strings (e.g., "min_count": "2"), by casting those values to numeric types before doing math.

Changes:

• Cast weight, drop_count, and min_count from grading policy entries to float/int when building the internal policy map.
• Add a unit-test scenario covering grading policies with string-typed numeric fields.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
lms/djangoapps/course_home_api/progress/api.py	Cast grading-policy numeric fields to float/int to prevent type errors during placeholder/math operations.
lms/djangoapps/course_home_api/progress/tests/test_api.py	Add a scenario where grading policy numeric fields are strings.

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[jansenk]

I don't disagree with this change but I wonder whether or not this should be made further up the chain of responsibility, like, should this be done in CourseBlock.set_grading_policy()?