B7: give Python ROC and TRIX constructor defaults

Every other Python momentum indicator (RSI, CCI, ...) carries a
#[pyo3(signature)] default, but ROC and TRIX required an explicit
period. Both now default to the TA-Lib convention (ROC period=10, TRIX
period=30), and the .pyi stubs reflect the defaults. Node and WASM
constructors deliberately stay explicit-only -- napi-rs and
wasm-bindgen do not support default arguments, and every constructor in
those bindings is uniformly explicit.

bindings/python/src/lib.rs

@@ -836,6 +836,7 @@ struct PyRoc {
 #[pymethods]
 impl PyRoc {
     #[new]
+    #[pyo3(signature = (period=10))]
     fn new(period: usize) -> PyResult<Self> {
         Ok(Self {
             inner: wc::Roc::new(period).map_err(map_err)?,
@@ -1054,6 +1055,7 @@ struct PyTrix {
 #[pymethods]
 impl PyTrix {
     #[new]
+    #[pyo3(signature = (period=30))]
     fn new(period: usize) -> PyResult<Self> {
         Ok(Self {
             inner: wc::Trix::new(period).map_err(map_err)?,