Auto merge of rust-lang#145352 - Shourya742:2025-08-12-remove-default-config, r=Kobzol

Remove default config from bootstrap

This PR removes the default config initialization from parse_inner, as it introduced many assumptions during config setup. Instead, each variable is now manually initialized to eliminate certain invariants in parse_inner and streamline the process.

r? `@Kobzol`

Author: bors