Restructure tokenizer module (#700)

* Remove duplicated tests

These tests already were copied to tokeniser2.rs, so removing them doesn't affect code coverage.

* Move tokeniser to its own module

Now there's a module for tokens, and the tokenizer/lexer implementation is private within the token module.

src/wasm-lib/tests/modify/main.rs

@@ -33,7 +33,7 @@ async fn setup(code: &str, name: &str) -> Result<(EngineConnection, Program, uui
         .commands_ws(None, None, None, None, Some(false))
         .await?;
 
-    let tokens = kcl_lib::tokeniser::lexer(code);
+    let tokens = kcl_lib::token::lexer(code);
     let parser = kcl_lib::parser::Parser::new(tokens);
     let program = parser.ast()?;
     let mut mem: kcl_lib::executor::ProgramMemory = Default::default();