fix memory leaks in generated bindings

This addresses a couple of issues:

- We weren't freeing canonical ABI results after calling imports and then
  converting the results to Python values.

- We were using the PyO3 `Bound` APIs incorrectly in a few places, resulting in
  refcounts being incremented too many times.

While debugging the latter issue, I took the opportunity to update to the latest
PyO3 release, which required addressing the usual API breakage.  It also
required temporarily forking the repo to add a patch to disable `extern
"C-unwind"` in `pyo3_ffi` on `wasm32`.  We should be able to drop that fork once
we upgrade everything to Python 3.14.

Finally, I discovered
https://pyo3.rs/v0.25.0/features.html#pyo3_disable_reference_pool which
supposedly optimizes Rust<->Python transitions by disabling a feature we don't
rely on anyway, so I went ahead and enabled it.

Fixes #152

Signed-off-by: Joel Dice <joel.dice@fermyon.com>

Author: dicej

Cargo.lock

@@ -22,7 +22,9 @@ wasmparser = "0.227.0"
 indexmap = "2.6.0"
 bincode = "1.3.3"
 heck = "0.5.0"
-pyo3 = { version = "0.22.5", features = [
+# TODO: switch back to upstream once we've updated to Python 3.14, at which
+# point the following patch will no longer be needed:
+pyo3 = { git = "https://github.com/dicej/pyo3", branch = "v0.25.0-no-wasm32-unwind", features = [
     "abi3-py39",
     "extension-module",
 ], optional = true }

Cargo.toml

@@ -124,9 +124,12 @@ fn package_all_the_things(out_dir: &Path) -> Result<()> {
         }
     }
 
-    cmd.env("RUSTFLAGS", "-C relocation-model=pic")
-        .env("CARGO_TARGET_DIR", out_dir)
-        .env("PYO3_CONFIG_FILE", out_dir.join("pyo3-config.txt"));
+    cmd.env(
+        "RUSTFLAGS",
+        "-C relocation-model=pic --cfg pyo3_disable_reference_pool",
+    )
+    .env("CARGO_TARGET_DIR", out_dir)
+    .env("PYO3_CONFIG_FILE", out_dir.join("pyo3-config.txt"));
 
     let status = cmd.status()?;
     assert!(status.success());

build.rs

@@ -9,7 +9,9 @@ crate-type = ["staticlib"]
 [dependencies]
 anyhow = "1.0.91"
 once_cell = "1.20.2"
-pyo3 = { version = "0.22.5", features = ["abi3-py312", "num-bigint"] }
+# TODO: switch back to upstream once we've updated to Python 3.14, at which
+# point the following patch will no longer be needed:
+pyo3 = { git = "https://github.com/dicej/pyo3", branch = "v0.25.0-no-wasm32-unwind", features = ["abi3-py312", "num-bigint"] }
 componentize-py-shared = { path = "../shared" }
 num-bigint = "0.4.6"
 wit-bindgen = { version = "0.40.0", default-features = false, features = ["macros", "realloc"] }