Enable use of cargo-fuzz without a separate workspace

This addresses #345.
Currently, `cargo-fuzz` defines an independent workspace

```
[workspace]
members = ["."]
```

which introduces some issues like caching setup, separate linting
configs, etc.

The main reason for this seems to be a custom config for
`profile.release.debug` which is allowed to be changed only at the
root Cargo.toml of the workspace. This commit adds a workaround
for that by supplying `--config profile.release.debug=true`.

In order to not break workflows of the existing users I introduced
a separate flag which defaults to the old behavior.

src/options/init.rs

@@ -8,6 +8,10 @@ pub struct Init {
     /// Name of the first fuzz target to create
     pub target: String,
 
+    #[arg(long, value_parser = clap::builder::BoolishValueParser::new(), default_value = "true")]
+    /// Whether to create a separate workspace for fuzz targets crate
+    pub create_workspace: Option<bool>,
+
     #[command(flatten)]
     pub fuzz_dir_wrapper: FuzzDirWrapper,
 }

src/project.rs

@@ -66,7 +66,11 @@ impl FuzzProject {
         let mut cargo = fs::File::create(&cargo_toml)
             .with_context(|| format!("failed to create {}", cargo_toml.display()))?;
         cargo
-            .write_fmt(toml_template!(manifest.crate_name, manifest.edition))
+            .write_fmt(toml_template!(
+                manifest.crate_name,
+                manifest.edition,
+                init.create_workspace
+            ))
             .with_context(|| format!("failed to write to {}", cargo_toml.display()))?;
 
         let gitignore = fuzz_project.join(".gitignore");
@@ -137,7 +141,7 @@ impl FuzzProject {
             .arg(&build.triple);
         // we default to release mode unless debug mode is explicitly requested
         if !build.dev {
-            cmd.arg("--release");
+            cmd.args(["--release", "--config", "profile.release.debug=true"]);
         }
         if build.verbose {
             cmd.arg("--verbose");

src/templates.rs

@@ -1,5 +1,5 @@
 macro_rules! toml_template {
-    ($name:expr, $edition:expr) => {
+    ($name:expr, $edition:expr, $create_workspace:expr) => {
         format_args!(
             r##"[package]
 name = "{name}-fuzz"
@@ -14,20 +14,22 @@ libfuzzer-sys = "0.4"
 
 [dependencies.{name}]
 path = ".."
-
-# Prevent this from interfering with workspaces
-[workspace]
-members = ["."]
-
-[profile.release]
-debug = 1
-"##,
+{workspace}"##,
             name = $name,
             edition = if let Some(edition) = &$edition {
                 format!("edition = \"{}\"\n", edition)
             } else {
                 String::new()
             },
+            workspace = if let Some(true) = $create_workspace {
+                r##"
+# Use independent workspace for fuzzers
+[workspace]
+members = ["."]
+"##
+            } else {
+                ""
+            }
         )
     };
 }
@@ -41,6 +43,7 @@ name = "{0}"
 path = "fuzz_targets/{0}.rs"
 test = false
 doc = false
+bench = false
 "#,
             $name
         )