Static evaluation of `CARGO_WORKSPACE_DIR` env var leaks to consumers.

[rcgoodfellow]

In the following code

falcon/ztest/src/lib.rs

Lines 298 to 337 in 29deea1

	pub fn copy_bin_to_zone(&self, name: &str, bin: &str) -> Result<()> {
	let profile = if cfg!(debug_assertions) {
	"debug"
	} else {
	"release"
	};
	let from = match env!("CARGO_WORKSPACE_DIR") {
	"" => format!("target/{}/{}", profile, bin),
	path => format!("{}target/{}/{}", path, profile, bin),
	};
	let to = format!("opt/{}", bin);
	self.copy_to_zone(name, &from, &to)
	}
	pub fn copy_workspace_to_zone(
	&self,
	name: &str,
	from: &str,
	to: &str,
	) -> Result<()> {
	let from = match env!("CARGO_WORKSPACE_DIR") {
	"" => from.into(),
	path => format!("{}{}", path, from),
	};
	self.copy_to_zone(name, &from, to)
	}
	pub fn copy_workspace_to_zone_recursive(
	&self,
	name: &str,
	from: &str,
	to: &str,
	) -> Result<()> {
	let from = match env!("CARGO_WORKSPACE_DIR") {
	"" => from.into(),
	path => format!("{}{}", path, from),
	};
	self.copy_to_zone_recursive(name, &from, to)
	}
	}

the falcon ztest library is evaluating CARGO_WORKSPACE_DIR at compile time. This check also happens in any crate that consumes ztest and then goes on to transitively impact all crates in a dependency tree involving ztest. This is highly undesirable behavior. Figure out a better way to find workspace binaries than the current approach.