configurable stack and heap memory size (#288)

- Allow configuration of the maximum heap and stack size via CLI flags
and JSON input settings.
- Increase the default value for the stack size to 32kb.

---------

Signed-off-by: Cyrill Leutwiler <bigcyrill@hotmail.com>

crates/llvm-context/src/polkavm/context/tests.rs

@@ -23,6 +23,7 @@ pub fn create_context(
         true,
         Default::default(),
         Default::default(),
+        Default::default(),
     )
 }