Don't add --release to cargo if --profile present

[messense]

I wonder if a separate --profile make sense vs. just using --cargo-extra-args

This is a fair point. Note that because maturin passes --release automatically in some contexts, the user cannot override the --profile without also figuring out how to invoke maturin to not pass the flag:

$ cargo build --release --profile dev
error: conflicting usage of --profile=dev and --release
The `--release` flag is the same as `--profile=release`.
Remove one flag or the other to continue.

Originally posted by @davidhewitt in #774 (comment)

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[messense]

We could add a warning/error here, but we can't differentiate --release from user input and default value of some commands here.