fix(clarity-cli): Make behavior of eval without .clar file less confusing

Closes #6496.

That issue reported that `clarity-eval SPWHATEVER something.clar`
hangs forever, but it turns out that that's only half true. What it's
in fact doing is waiting for `stdin` input.

The Clarity program file name is an optional argument, and if it's not
given, the program is read from the standard input instead. In the above
example command line, `something.clar` is interpreted as the VM state DB
directory instead (which is obviously not the caller's intention).

I made three changes:

- The usage message now uses the common format where all optional args
  are wrapped in square brackets and required args are unwrapped:

  ```
  Usage: clarity-cli eval [--costs] [--epoch E] [--clarity_version N] contract-identifier [program.clar] vm-state.db
  ```
- I also added the info to the help message that without the
  `program.clar`, things will be read from `stdin`.
- And I changed the order of execution so that the contract ID and the
  VM DBs are handled first, before the program content is loaded. That
  way, if the user passes a `something.clar` but (incorrectly) leaves
  off one of the required args, it immediately causes an error, instead
  of waiting for the program from `stdin` and *then* erroring.

I also fixed the VSCode launch settings for clarity-cli.

Author: benjamin-stacks

.vscode/launch.json

@@ -27,7 +27,7 @@
         "args": [
           "build",
           "--bin=clarity-cli",
-          "--package=stackslib"
+          "--package=clarity-cli"
         ],
         "filter": {
           "name": "clarity-cli",

contrib/clarity-cli/src/lib.rs

@@ -790,14 +790,26 @@ impl HeadersDB for CLIHeadersDB {
 fn get_eval_input(invoked_by: &str, args: &[String]) -> EvalInput {
     if args.len() < 3 || args.len() > 4 {
         eprintln!(
-            "Usage: {invoked_by} {} [--costs] [--epoch E] [--clarity_version N] [contract-identifier] (program.clar) [vm-state.db]",
+            "Usage: {invoked_by} {} [--costs] [--epoch E] [--clarity_version N] contract-identifier [program.clar] vm-state.db",
             args[0]
         );
+        eprintln!();
+        eprintln!("  If a program file name is not provided, the program is read from stdin.");
         panic_test!();
     }
 
     let vm_filename = if args.len() == 3 { &args[2] } else { &args[3] };
 
+    let contract_identifier = friendly_expect(
+        QualifiedContractIdentifier::parse(&args[1]),
+        "Failed to parse contract identifier.",
+    );
+
+    let marf_kv = friendly_expect(
+        MarfedKV::open(vm_filename, None, None),
+        "Failed to open VM database.",
+    );
+
     let content: String = {
         if args.len() == 3 {
             let mut buffer = String::new();
@@ -814,16 +826,6 @@ fn get_eval_input(invoked_by: &str, args: &[String]) -> EvalInput {
         }
     };
 
-    let contract_identifier = friendly_expect(
-        QualifiedContractIdentifier::parse(&args[1]),
-        "Failed to parse contract identifier.",
-    );
-
-    let marf_kv = friendly_expect(
-        MarfedKV::open(vm_filename, None, None),
-        "Failed to open VM database.",
-    );
-    // return (marf_kv, contract_identifier, vm_filename, content);
     EvalInput {
         marf_kv,
         contract_identifier,