Make rng in TestEnv deterministic and seedable (#461)

* Move three dependent customizations into new file

* default_min_pin_length(_rp_ids) and max_rp_ids_length

* Did some backing store tricks to make the list configurable in
  TestCustomization.

* Add testing for TestCustomization

* Change assert comparison to assert_eq

* Separate tests

* Move 3 pure constants to new file

* Return Vec<String> for rp_ids()

* Make rng in TestEnv deterministic and seedable

* Move seed method to TestRng256

* Change some constant name in comments to snake case

* Move seed rng of env to the start

* Fix unused warning

* Make rng in TestEnv deterministic and seedable

* Move seed method to TestRng256

* Move seed rng of env to the start

* Fix unused warning

* Seed rng in all fuzz targets

* Fix error introduced when merging

Co-authored-by: Julien Cretin <cretin@google.com>

fuzz/fuzz_targets/fuzz_target_process_ctap2_get_assertion.rs

@@ -7,5 +7,5 @@ use libfuzzer_sys::fuzz_target;
 // For a more generic fuzz target including all CTAP commands, you can use
 // fuzz_target_process_ctap_command.
 fuzz_target!(|data: &[u8]| {
-    process_ctap_specific_type(data, InputType::CborGetAssertionParameter);
+    process_ctap_specific_type(data, InputType::CborGetAssertionParameter).ok();
 });