Provide a user-friendly error message when Cargo.toml is not found

[imotai]

Description:

When running cargo-prove prove build and Cargo.toml is not found in the current directory or any parent directory, the current error message is:

thread 'main' panicked at cli/src/build.rs:27:40:
called `Result::unwrap()` on an `Err` value: CargoMetadata { stderr: "error: could not find `Cargo.toml` in `/mnt/ssd3/opensource` or any parent directory\n" }
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Suggestion:

Instead of the current error message, we can follow the error message from cargo build

error: could not find `Cargo.toml` in `/mnt/ssd3/opensource` or any parent directory

Related code

sp1/cli/src/build.rs

Lines 25 to 28 in f50fb1c

	pub fn build_program(args: &BuildArgs) -> Result<Utf8PathBuf> {
	let metadata_cmd = cargo_metadata::MetadataCommand::new();
	let metadata = metadata_cmd.exec().unwrap();
	let root_package = metadata.root_package();

[varun-doshi]

Hi...I'd like to work on this issue

[4rgon4ut]

@varun-doshi its been a while so I decided to stab, hope its ok