chore: initialize NexaCore compiler workspace with basic frontend and CLI

Add initial project structure for NexaCore programming language compiler:
- Create Cargo workspace with 4 crates (cli, driver, frontend, runtime)
- Add lexer with indentation-based tokenization and keyword support
- Add parser for modules, functions, structs, and basic expressions
- Implement CLI with build command and placeholder subcommands
- Add driver crate to orchestrate compilation pipeline
- Include .gitignore for Rust build

Cargo.toml

@@ -0,0 +1,15 @@
+[workspace]
+members = [
+    "crates/nxc-cli",
+    "crates/nxc-driver",
+    "crates/nxc-frontend",
+    "crates/nxc-runtime",
+]
+resolver = "2"
+
+[workspace.package]
+edition = "2021"
+license = "Apache-2.0"
+version = "0.1.0"
+authors = ["NexaCore Contributors"]
+