This commit enhances the series type handling in `src/ast/rtl/series.rs`
by introducing helper methods `as_float` and `as_int` in
`src/ast/types.rs` to manage type conversions more robustly.
It also updates the function overload resolution in `src/ast/types.rs`
to prioritize exact parameter matches before falling back to implicit
coercions.
Finally, the example `err.myc` has been updated to reflect a more
accurate implementation of a Simple Moving Average (SMA) calculation.
Michael Schimmel
7b6f6e52bd