Fix nondeterministic crash on pku flags (#170)

* Fix nondeterministic crash on pku flags

When V8 is initialized on a non-main thread on CPU architectures that
have PKU enabled, rendering can occasionally crash during memory
allocation:

```
Thread 36 "python" received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7fff69e006c0 (LWP 134254)]
0x00007ffff2f728b1 in v8::internal::FreeListManyCachedFastPathBase::Allocate(unsigned long, unsigned long*, v8::internal::AllocationOrigin) ()
```

When this happens a SIGSEGV is thrown in the V8 isolate itself, which is
caught by neither Rust not Python so the application exits with no
further context about the issue.

* Run additional tests after labels are added

* Fix all rust tests to initialize v8 platform

Fix clearing correct modules after reload (#168)

Merge pull request #154 from piercefreeman/feature/force-cast-excepti…

…ons-to-json

Override default response type for APIExceptions

Merge pull request #151 from piercefreeman/feature/optional-db-deps

Remove database modules

Merge pull request #150 from piercefreeman/feature/url-polyfills

Add polyfills for missing URL/QueryParams on server

Merge pull request #149 from piercefreeman/bug/fix-relative-url

Pass fallback origin to JS URL

Merge pull request #147 from piercefreeman/feature/typehint-unprocess…

…able-entity

Structure 422 unprocessable entities & support typehinted headers

Merge pull request #146 from piercefreeman/feature/shared-superclass-…

…tests

Test suite for global models and interfaces

Merge pull request #145 from piercefreeman/feature/shared-superclass-…

…models

Global models and interface hierarchy

Merge pull request #144 from piercefreeman/feature/pin-twine-metadata…

…-to-2-3

Pin maturin to use metadata 2.3