util: fix inspecting URL subclass prototypes

[HoonDongKang]

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

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.49%. Comparing base (f88a1d2) to head (83ea3a3).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #66822      +/-   ##
==========================================
- Coverage   90.49%   90.49%   -0.01%     
==========================================
  Files         797      797              
  Lines      277780   277780              
  Branches    53360    53359       -1     
==========================================
- Hits       251388   251367      -21     
- Misses      16791    16804      +13     
- Partials     9601     9609       +8     

Files with missing lines	Coverage Δ
lib/internal/util/inspect.js	97.04% <100.00%> (ø)

... and 28 files with indirect coverage changes

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[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/78464/