fix(tt_tool): vary RT_MAX_LAYER per tech

Each tech has a different metal stackup, so user projects get a different top routing metal layer. tt-support-tools now handles this instead of the user having to worry about this when switching PDKs.

project.py

@@ -482,6 +482,7 @@ class Project:
             "VERILOG_FILES": [f"dir::{src}" for src in self.sources],
             "DIE_AREA": die_area,
             "FP_DEF_TEMPLATE": def_template,
+            "RT_MAX_LAYER": self.tech.project_top_metal_layer,
         }
         write_config(config, os.path.join(self.src_dir, "user_config"), ("json",))
 

tech.py

@@ -18,6 +18,7 @@ class Tech(Protocol):
     tt_corner: str
     cell_regexp: str
     netlist_type: Literal["pnl", "nl"]
+    project_top_metal_layer: str
 
     """ These layers will be removed from the SVG render of the layout """
     label_layers: List[Tuple[int, int]]
@@ -43,6 +44,7 @@ class Sky130Tech(Tech):
     tt_corner = "nom_tt_025C_1v80"
     cell_regexp = r"sky130_(?P<cell_lib>\S+)__(?P<cell_name>\S+)_(?P<cell_drive>\d+)"
     netlist_type = "pnl"
+    project_top_metal_layer = "met4"
     label_layers = [
         (64, 59),  # pwell.label
         (64, 5),  # nwell.label
@@ -94,6 +96,7 @@ class IHPTech(Tech):
     tt_corner = "nom_typ_1p20V_25C"
     cell_regexp = r"sg13g2_(?P<cell_name>\S+)_(?P<cell_drive>\d+)"
     netlist_type = "nl"
+    project_top_metal_layer = "Metal5"
     label_layers = [
         (8, 1),  # Metal1.label
         (8, 25),  # Metal1.text