feat: add benchmarks and enhance LSP completions/hover

Benchmarks:
- Add fib, list_ops, primes benchmarks comparing Lux vs Node.js vs Rust
- Lux matches Rust performance and is 8-30x faster than Node.js
- Add docs/benchmarks.md documenting results

LSP improvements:
- Context-aware completions (module access vs general)
- Add List, String, Option, Result, Console, Math method completions
- Add type and builtin completions
- Hover now shows type signatures and documentation for known symbols
- Hover returns formatted markdown with code blocks

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

benchmarks/fib.lux

@@ -0,0 +1,10 @@
+// Fibonacci benchmark - recursive implementation
+fn fib(n: Int): Int = {
+    if n <= 1 then n
+    else fib(n - 1) + fib(n - 2)
+}
+
+fn main(): Unit = {
+    let result = fib(35)
+    Console.print("fib(35) = " + toString(result))
+}