fix: Use floats when displaying card intervals

[Luc-Mcgrady]

Linked issue (required)

fixes #4787

Summary / motivation (required)

While it is impossible during normal use to get an interval greater than 10 years due to the max_interval. By using set date you can get a larger interval which is then displayed incorrectly. By using a float to store the second values instead of a u32, we can display higher values (although the day interval is still constrained by u32).

Steps to reproduce (required, use N/A if not applicable)

1. use set interval with a massive number
2. check the

How to test (required)

Follow the steps to reproduce. The number will display as the actual interval in all instances.

Checklist (minimum)

• I ran ./ninja check or an equivalent relevant check locally.
• I added or updated tests when the change is non-trivial or behavior changed.

Details

Before / after behavior (optional)

Risk / compatibility / migration (optional)

Since the value is at max MAX_u32 * 86_400 maybe we should use a u64 instead? largely a moot point as accuracy doesn't matter for the time display functions.

UI evidence (required for visual changes; otherwise N/A)

Scope

• This PR is focused on one change (no unrelated edits).