feat[venom]: tune function inliner (#4584)

this commit tunes the function inliner by assigning `param` and `ret`
instructions a cost of 0 (in fact, they should probably have negative
cost, since those only have cost in the call convention overhead, but
when inlined, they disappear).

Author: charles-cooper

vyper/venom/basicblock.py

@@ -402,6 +402,8 @@ def remove_phi_operand(self, label: IRLabel) -> None:
 
     @property
     def code_size_cost(self) -> int:
+        if self.opcode in ("ret", "param"):
+            return 0
         if self.opcode == "store":
             return 1
         return 2