Fix decoder generation for external nested addressable components and add max-decode-depth parameter (#12)

* Initial plan

* Fix bus decoder to skip external nested components

Co-authored-by: arnavsacheti <36746504+arnavsacheti@users.noreply.github.com>

* Optimize external children check using generator expressions

Co-authored-by: arnavsacheti <36746504+arnavsacheti@users.noreply.github.com>

* Add max-decode-depth CLI argument

Added --max-decode-depth argument that:
- Is added to CLI arguments in __peakrdl__.py
- Piped into design state via ExporterKwargs and DesignStateKwargs
- Used to control max depth in listener.py
- All 66 tests pass including new test for the parameter

Co-authored-by: arnavsacheti <36746504+arnavsacheti@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: arnavsacheti <36746504+arnavsacheti@users.noreply.github.com>

src/peakrdl_busdecoder/exporter.py

@@ -27,6 +27,7 @@ class ExporterKwargs(TypedDict, total=False):
     address_width: int
     cpuif_unroll: bool
     reuse_hwif_typedefs: bool
+    max_decode_depth: int
 
 
 if TYPE_CHECKING:
@@ -84,6 +85,9 @@ class BusDecoderExporter:
         cpuif_unroll: bool
             Unroll arrayed addressable nodes into separate instances in the CPU
             interface. By default, arrayed nodes are kept as arrays.
+        max_decode_depth: int
+            Maximum depth for address decoder to descend into nested addressable
+            components. By default, the decoder descends 1 level deep.
         """
         # If it is the root node, skip to top addrmap
         if isinstance(node, RootNode):