Cargo `+toolchain` commands are not rewritten or filtered

Bug

Cargo commands using rustup's +toolchain syntax are not recognized by the current rewrite path. Support for these commands was previously added in #99, including cargo +nightly test, but the behavior is not present in RTK 0.44.2.

Steps to reproduce

Tested with RTK 0.44.2 on macOS:

$ rtk rewrite "cargo +stable check"
$ echo $?
1

$ rtk hook check "cargo +stable check"
No rewrite for: cargo +stable check

In a crate containing a compilation error, compare:

rtk cargo check
rtk cargo +stable check

Actual behavior

rtk cargo check applies the Cargo filter and produces compact output:

cargo check: 1 errors, 0 warnings (1 crates)

rtk cargo +stable check executes the command but produces unfiltered Cargo output.

Expected behavior

rtk rewrite should recognize Cargo commands with a +toolchain selector, preserve the selector, and route the Cargo subcommand through the same output filter used without a selector.

This affects filtered subcommands such as build, check, clippy, and test.

Start by reproducing the issue with rtk rewrite "cargo +stable check" and rtk hook check "cargo +stable check", then trace the Cargo command rewrite path. Verify that selectors such as +stable and +nightly are preserved and that filtered subcommands including build, check, clippy, and test produce the same compact output as commands without a selector.