Refactor: Introduce system library

- Add `rtl/system.myc` as the system library, containing core utilities
  like `while` and `cache`.
- Remove the duplicate `prelude.myc` from `src/ast/rtl/`.
- Modify `Environment::collect_dependencies` to implicitly add `#use
  system` when necessary.
- Update `Environment::with_cwd` to also add the `rtl` subdirectory to
  search paths.
- Add `target/` to `.geminiignore` to exclude build artifacts.
- Adjust example `sma.myc` to use the new `cache` macro and reduce
  sample data size.
- Update `rtl/sma.myc` to correctly initialize the `history` series with
  its `length`.
- Add `preload_dependencies` calls to `dump_ast` and `run_script` for
  proper module loading.

src/ast/rtl/prelude.myc

@@ -1,31 +0,0 @@
-;; Myc Prelude
-;; This file is evaluated during Environment bootstrapping.
-;; It contains standard macros and functions.
-
-(macro while [cond body]
-  `((fn [] (if ~cond
-             (do ~body (again))
-           )))
-)
-
-;; Creates a stateful cache (Series) from a stateless stream.
-;; 
-;; Pipes are highly optimized, stateless stream-routers that do not allocate memory 
-;; for historical data. If multiple indicators need to read historical data from 
-;; a stream, or if you need to access previous items via index (e.g. `(my_data 5)`), 
-;; you must explicitly cache the stream.
-;;
-;; Parameters:
-;;   lookback: The maximum number of items to keep in memory (e.g. 100).
-;;   type:     The data type or schema of the series (e.g. :float or {:price :float}).
-;;   src:      The source stream to observe and cache.
-;;
-;; Returns:
-;;   A stateful Series object that automatically updates when the source stream fires.
-(macro cache [lookback type src]
-  `(do
-     (def data (series ~lookback ~type))
-     (pipe [~src] (fn [s] (do (push data s))))
-     data
-   )
-)