util: fix inspecting URL subclass prototypes - #66822

Inspecting a URL subclass prototype throws a TypeError:

const { inspect } = require('node:util');

class TestURL extends URL {}

inspect(TestURL.prototype);
// TypeError: Receiver must be an instance of class URL

isURL() accessed value.href before checking instanceof URLand it invokes the getter on this prototype.

Use isURLInstance() to check for URL internal state before reading href:

- return typeof value.href === 'string' && value instanceof internalUrl.URL;
+ return internalUrl.isURLInstance(value) && typeof value.href === 'string';

The check returns false for subclass prototypes without invoking the getter, allowing inspection to continue through the generic object formatting path.

Add regression tests for subclass prototypes, class references inspected with showHidden: true, and %o formatting. Also cover normal subclass instances and an overridden href getter returning undefined with customInspect: false.

Fixes: #66821
Assisted-by: Codex:6.1-sol-high