Fixes Rust code generation for single file output when using namespaces (#8877)

* Adds tests for Rust single file mode

All existing tests only compile Rust code using --rust-module-root-file.

* Adds standalone include tests for Rust

The imports for these tests have been moved to their own file, as the existing intergration_test.rs file hides compilation issues from code generation due to symbols brought into scope outside of the generated code (e.g. `extern crate alloc`).

* Declare alloc crate in every Rust namespace

When performing code generation within a single file, extern crate alloc needs to be delcared to bring alloc into scope within every inner namespace.

* Regenerates generated schemas

scripts/generate_code.py

@@ -85,6 +85,11 @@ RUST_OPTS = BASE_OPTS + [
     "--gen-name-strings",
     "--rust-module-root-file",
 ]
+RUST_STANDALONE_OPTS = BASE_OPTS + [
+    "--rust",
+    "--gen-all",
+    "--gen-name-strings",
+]
 RUST_SERIALIZE_OPTS = BASE_OPTS + [
     "--rust",
     "--gen-all",
@@ -288,6 +293,12 @@ flatc(
     schema="include_test/include_test1.fbs",
 )
 
+flatc(
+    RUST_STANDALONE_OPTS,
+    include="include_test",
+    schema="include_test/include_test1.fbs",
+)
+
 flatc(
     RUST_OPTS,
     prefix="include_test2",
@@ -295,6 +306,12 @@ flatc(
     schema="include_test/sub/include_test2.fbs",
 )
 
+flatc(
+    RUST_STANDALONE_OPTS,
+    include="include_test",
+    schema="include_test/sub/include_test2.fbs",
+)
+
 flatc(
     BINARY_OPTS + ["--bfbs-filenames", str(tests_path)],
     include="include_test",