RustCrypto provider patch

Source: crates.io str0m-rust-crypto 0.6.0, upstream revision 9b159720be773693dd561dec0fb20c6d7e4aa323 from algesten/str0m. The source is used under its MIT option; the upstream copyright and license are in LICENSE-MIT.txt. Cargo.toml.orig preserves the published, unnormalized manifest.

The archived probe workspace selects this copy through [patch.crates-io]. It makes two changes:

1. Move dimpl/rcgen behind the default-enabled generate-cert feature. With that feature disabled, generate_certificate() returns None and callers must supply a certificate through RtcConfig::set_dtls_cert.
2. Explicitly select dimpl's RustCrypto provider when constructing DTLS.

The probe disables default features and supplies a host-generated ECDSA P-256 certificate. The maintained firmware generates certificates on the ESP32 using mbedTLS. The upstream certificate generator enables AWS-LC, whose C headers reject Xtensa. Disabling it avoids that native dependency; fingerprint verification and normal DTLS authentication remain enabled.

provider.patch records the diff against the published crate. Keep changes confined to this purpose. When upgrading, compare upstream first and remove the patch when equivalent feature controls and provider selection are available. Check the selected dependency graph, rebuild the archived host publisher and rerun its SFU interoperability probe.