refactor: split ecr into library and cli crates

The root package becomes a virtual workspace: `crates/ecr` holds the
library (package name `ecr`) and `crates/ecr-cli` the command line
front-end, which keeps installing the `ecr` binary. No behavior change.

The library must not depend on CLI types, so mount::setup_mounts now
takes the `no_bind` flag instead of a `&Args`.

Cargo.lock

@@ -302,7 +302,6 @@ version = "0.1.0"
 dependencies = [
  "anyhow",
  "base64",
- "clap",
  "cpio",
  "dirs",
  "flate2",
@@ -323,6 +322,17 @@ dependencies = [
  "zstd",
 ]
 
+[[package]]
+name = "ecr-cli"
+version = "0.1.0"
+dependencies = [
+ "anyhow",
+ "clap",
+ "dirs",
+ "ecr",
+ "tempfile",
+]
+
 [[package]]
 name = "either"
 version = "1.16.0"