♻️ Drop assert imports from doc fences

`assert` is the sole injected exception: the generated test always binds
it, so a fence must not import it. Revert the README imports and the
generator's node:assert merging; the fences keep the assigned variables
and `assert.equal` calls, and the generator again rejects a fence that
imports node:assert.

README.md

@@ -47,7 +47,6 @@ builder. Calling the builder with a handler map keyed by `T`'s members returns a
 matcher: a function from `T` to the common return type.
 
 ```ts
-import { strict as assert } from "node:assert";
 import { getPrimitiveUnionMatcher } from "tiny-pattern-ts";
 
 const matchAnswer = getPrimitiveUnionMatcher<"yes" | "no">();
@@ -65,7 +64,6 @@ Add a fallback as the second argument to leave members unhandled; the fallback
 receives the remainder:
 
 ```ts
-import { strict as assert } from "node:assert";
 import { getPrimitiveUnionMatcher } from "tiny-pattern-ts";
 
 const matchLabel = getPrimitiveUnionMatcher<"yes" | "no" | "maybe">();
@@ -92,7 +90,6 @@ function takes the discriminant property's name and returns the handler-map
 builder, keyed by that property's tags.
 
 ```ts
-import { strict as assert } from "node:assert";
 import { getTaggedUnionMatcher } from "tiny-pattern-ts";
 
 type Shape =