fix: update hole_diameter default value to 0.3mm in pcb_via

[rushabhcodes]

This pull request makes a minor update to the default value for the hole_diameter property in the pcb_via schema, increasing it from 0.25mm to 0.3mm for consistency.

[techmannih]

You also need to make them optional. I think you have added them optional in props

[rushabhcodes]

@techmannih

outer_diameter: distance.default("0.6mm")

• The field must exist.
• If the user does not provide a value, it will automatically be set to "0.6mm".
• The resulting object will always contain a value for outer_diameter.

outer_diameter: distance.default("0.6mm").optional()

• The field is optional.
• If omitted, the value will be undefined (not "0.6mm").
• The default only applies if the field is present, but its value is undefined or invalid (depending on the library).

[seveibar]

the defaults really shouldn't be inside circuit-json at all, we should remove the defaults

[rushabhcodes]

Where should i defaults then??