Vendor crabrl-fork source and remove submodule linkage

- Replace `rust/crabrl-fork` gitlink with tracked source files
- Add workspace notes documenting why the fork is vendored
- Update ignore rules for vendored fork build artifacts

rust/crabrl-fork/examples/benchmark_single.rs

@@ -0,0 +1,36 @@
+//! Single file benchmark
+
+use crabrl::Parser;
+use std::env;
+use std::fs;
+use std::time::Instant;
+
+fn main() {
+    let args: Vec<String> = env::args().collect();
+    if args.len() != 2 {
+        eprintln!("Usage: {} <xbrl-file>", args[0]);
+        std::process::exit(1);
+    }
+
+    let content = fs::read(&args[1]).expect("Failed to read file");
+
+    let parser = Parser::new();
+    let start = Instant::now();
+
+    match parser.parse_bytes(&content) {
+        Ok(document) => {
+            let elapsed = start.elapsed();
+            println!(
+                "Parsed in {:.3}ms: {} facts, {} contexts, {} units",
+                elapsed.as_secs_f64() * 1000.0,
+                document.facts.len(),
+                document.contexts.len(),
+                document.units.len()
+            );
+        }
+        Err(e) => {
+            eprintln!("Parse error: {}", e);
+            std::process::exit(1);
+        }
+    }
+}