chore: update tstyche to v7 (#16851)

### What?

This PR updates TSTyche to v7 (the latest).

### Why?

As usual, the latest version includes bug fixes and improvements. For
instance, TSTyche 7 falls back to TypeScript 6 when TS 7 is installed.
It does not support TS 7 yet, because of missing programmatic API. But
it is not a blocker if you would like to upgrade `typescript` at some
point.

---

TSTyche 4 release notes: https://tstyche.org/releases/tstyche-4
- applicable: primitive type matchers like `.toBeNever()` are removed in
favour of `.toBe<never>()`

TSTyche 5 release notes: https://tstyche.org/releases/tstyche-5
- applicable: the `.toBeAssignableWith()` matcher is renamed to
`.toBeAssignableFrom()`; the `checkDeclarationFiles` option is enabled
by default

TSTyche 6 release notes: https://tstyche.org/releases/tstyche-6

TSTyche 7 release notes: https://tstyche.org/releases/tstyche-7
- applicable: default configuration file location has changed. Now
`./tstyche.json` is loaded instead of `./tstyche.config.json`.

Signed-off-by: mrazauskas <tom@mrazauskas.de>

tstyche.json

@@ -0,0 +1,5 @@
+{
+  "$schema": "./node_modules/tstyche/schemas/config.json",
+  "checkDeclarationFiles": false,
+  "testFileMatch": ["test/**/types.spec.ts", "test/**/r2-types.spec.ts"]
+}