Switch to minimum supported Rust version compatible resolver

The url 2.5.4+ crate pulls idna 1.x -> idna_adapter -> icu_* 2.2.0, which
require rustc 1.86. A fresh dependency resolution (e.g. the Docker build,
which did not pass --locked) would select those and fail against the 1.85.0
toolchain pinned in rust-toolchain.toml. This patch bump the workspace to
resolver to fix this issue.

Note that as `ext/crr` uses Rust nightly that does not support the new
resolver, we had to add configure the projects as workspaces, to avoid `cargo`
dicovering the unsupported resolver in top-level Cargo.toml.