Make the Requested amount field accepts locale formated values

[frjo]

Fixes #4628

Add custom to_python() function to allow localised number inputs to Requested amount field. Add custom prepare_value() to make the widget use the locale correct decimal separator.

Test Steps

• Try saving all number format you know about. 10000 can in different countries be written as "10 000", "10000.00", "10 000,00", "10.000,00", "10,000.00". They should all be saved as "10000" in the database.
• Try to set the site to different locales and combine with different number format. All combinations should work.

[frjo]

I used up a lot of Claude code tokens for this 😄. So many nitty gritty details but after hours of testing I believe (hope) it's working.

Really needs testing by other people, important that this does not mess up users data.

If we can be sure it works I think it will be a nice ux improvement, allowing users to enter values the way they are used to and Hypha takes care of the rest.

[frjo]

@bmispelon I heard you created a solution for this already. Something similar to above or did you find a cleaner fix for it?