Split up `number` into `float` and `integer` for attributes

right now we only have `number`: https://github.com/getsentry/sentry-conventions/blob/253b600b1eddbfc98dd02684440738ee877c4f6f/schemas/attribute.schema.json#L51

but we should probably expand it to be `int` vs. `float`. I'll make the change.

_Originally posted by @AbhiPrasad in https://github.com/getsentry/sentry-conventions/pull/68#discussion_r2190886299_
            