Fix Rust UB problems (#6393)

* Fix miri problems by assuming alignment is 1 in rust

* Removed is_aligned fn from rust verifier.

* Add back is_aligned, but make it w.r.t. buffer[0]

* touch unused variable

* touch unused variable

* +nightly

* Move Rust miri testing into its own docker

* fix bash

* missing one endian conversion

* fix endianness2

* format stuff

Co-authored-by: Casper Neo <cneo@google.com>

tests/rust_usage_test/tests/flexbuffers_tests/binary_format.rs

@@ -108,6 +108,7 @@ fn store_vec_uint_16() {
     );
 }
 
+#[cfg(not(miri))]  // slow.
 quickcheck! {
     fn qc_f32(x: f32) -> bool {
         let fxb = singleton(x);

tests/rust_usage_test/tests/flexbuffers_tests/mod.rs

@@ -15,5 +15,6 @@
 mod binary_format;
 mod interop;
 mod other_api;
+#[cfg(not(miri))]  // slow.
 mod qc_serious;
 mod rwyw;

tests/rust_usage_test/tests/flexbuffers_tests/other_api.rs

@@ -13,9 +13,11 @@
 // limitations under the License.
 
 use flexbuffers::*;
+#[cfg(not(miri))]  // slow.
 use quickcheck::QuickCheck;
 
 #[test]
+#[cfg(not(miri))]  // slow.
 fn qc_reader_no_crash() {
     fn no_crash(xs: Vec<u8>) -> bool {
         let r = Reader::get_root(&xs);

tests/rust_usage_test/tests/flexbuffers_tests/rwyw.rs

@@ -14,6 +14,7 @@
 
 // Read what you wrote.
 use flexbuffers::*;
+#[cfg(not(miri))]  // slow.
 use quickcheck;
 use serde::{Deserialize, Serialize};
 
@@ -33,6 +34,7 @@ impl quickcheck::Arbitrary for NonNullString {
     }
 }
 
+#[cfg(not(miri))]  // slow.
 quickcheck! {
     fn qc_vec_bool(xs: Vec<bool>) -> bool {
         let mut builder = Builder::default();
@@ -363,6 +365,8 @@ struct Foo {
     c: Vec<u32>,
     d: String,
 }
+
+#[cfg(not(miri))]  // slow.
 quickcheck! {
     fn serde_foo(a: i8,
     b: f64,