Auto merge of #125004 - pymongo:issue-125002, r=estebank

Fix println! ICE when parsing percent prefix number

This PR fixes #125002 ICE occurring, for example, with `println!("%100000", 1)` or `println!("%    100000", 1)`.

## Test Case/Change Explanation

The return type of `Num::from_str` has been changed to `Option<Self>` to handle errors when parsing large integers fails.

1. The first `println!` in the test case covers the change of the first `Num::from_str` usage in `format_foreign.rs:426`.
2. The second `println!` in the test case covers the change of the second `Num::from_str` usage in line 460.
3. The 3rd to 5th `Num::from_str` usages behave the same as before.

The 3rd usage would cause an ICE when `num > u16::MAX` in the previous version, but this commit does not include a fix for the ICE in `println!("{:100000$}")`. I think we need to emit an error in the compiler and have more discussion in another issue/PR.

Author: bors