feat: Add a --profile option to choose a cargo profile

[sourcefrog]

Fixes #338

[sourcefrog]

This seems to currently fail baseline tests when run on itself, but not when the tests are run outside of mutants:

test well_tested_tree_finds_no_problems ... ok

failures:

---- hang_avoided_by_build_timeout_with_cap_lints stdout ----
thread 'hang_avoided_by_build_timeout_with_cap_lints' panicked at /home/mbp/.cargo/registry/src/index.crates.io-6f17d22bba15001f/assert_cmd-2.0.0/src/assert.rs:124:9:
Unexpected return code, failed var == 3
└── var: 4

command=`cd "/tmp/.tmpo0X0V9" && env -u RUST_BACKTRACE "/tmp/cargo-mutants-mutants-c1AEL6.tmp/target/mutants/cargo-mutants" "mutants" "--build-timeout-multiplier=4" "--regex=const" "--cap-lints=true"`
code=4
stdout=```"Found 1 mutant to test\nFAILED   Unmutated baseline in 0.1s build\n\n*** baseline\n\n*** /home/mbp/.rustup/toolchains/beta-x86_64-unknown-linux-gnu/bin/cargo test --no-run --verbose --manifest-path /tmp/cargo-mutants-.tmpo0X0V9-KZk1eU.tmp/Cargo.toml\nerror: failed to run `rustc` to learn about target-specific information\n\nCaused by:\n  process didn\'t exit successfully: `/home/mbp/.rustup/toolchains/beta-x86_64-unknown-linux-gnu/bin/rustc - --crate-name ___ --print=file-names \'\' --cap-lints=warn --crate-type bin --crate-type rlib --crate-type dylib --crate-type cdylib --crate-type staticlib --crate-type proc-macro --print=sysroot --print=split-debuginfo --print=crate-name --print=cfg` (exit status: 1)\n  --- stderr\n  error: multiple input filenames provided (first two filenames are `-` and ``)\n\n\n*** result: Failure(101)\n\n"```
stderr=```"ERROR cargo build failed in an unmutated tree, so no mutants were tested\n"```

note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

This error also occurs when I use cargo-mutants main branch to test this tree, and even with the profile removed from .cargo/mutants.toml.

Actually, maybe this is a separate existing (intermittent?) error?

Fixed in #399, I think.