feat: support both v4 and v5

[cesco69]

Adds dual Express 4/5 support through a new version option in the constructor. Default behavior remains on Express 4:

const express = require("ultimate-express");

// Express 4 behavior (default)
const app = express(); // or express({ version: 4 })

// Express 5 behavior
const app = express({ version: 5 });

Motivation

Express 5 is now the dominant version in the ecosystem:

Version	Downloads (Last 7 Days)	Tag
5.2.1	42,541,731	latest
4.22.2	20,748,526	latest-4

With Express 5 having more than double the weekly downloads compared to v4, it's important for ultimate-express to support both. In a future major version we may deprecate and remove v4 behavior entirely.

Full list of Express 5 changes implemented

Every behavioral divergence listed below is tested against express5 (npm:express@5) in the tests/tests/v5/ directory using the SKIP_V4 marker.

Removed APIs (throw on use)

Change	Test file	Behavior
app.del() removed	app-del-removed.js	Throws error, use app.delete()
app.param(fn) removed	app-param-fn-removed.js	Throws error, use app.param(name, fn)
req.param() removed	req-param-removed.js	Throws error, use req.params/req.body/req.query

Behavioral changes

Change	Test file	Behavior
Async error handling	async-errors-native.js	Rejected promises in handlers auto-forward to error middleware
res.status() validation	res-status-validation.js	Only accepts integers 100-999, throws RangeError otherwise
res.vary() validation	res-vary-throws.js	Throws when called without field argument
res.redirect('back') removed	res-redirect-back-removed.js	Treats 'back' as literal URL (no Referrer magic)
res.location('back') removed	res-redirect-back-removed.js	Same as above
req.query read-only	req-query-readonly.js	Assignment silently ignored, getter always returns parsed query
req.host includes port	req-host-port.js	Returns host:port instead of just host
req.params null prototype	req-params-prototype.js	No inherited Object methods (toString, hasOwnProperty, etc.)
res.clearCookie ignores maxAge/expires	res-clearCookie.js	User-provided maxAge/expires are overridden
express.urlencoded() default extended: false	urlencoded-default.js	Simple query parser by default (no nested objects)
express.static() dotfiles default 'ignore'	static-dotfiles.js	Dot-files and dot-directories return 404
app.listen() error handling	app-listen-error.js	Passes error to callback instead of throwing

Path route matching (new syntax)

Change	Test file	Behavior
Named wildcards /*splat	path-matching-splat.js	Wildcard must have a name, captures as array
Root-matching wildcard /{*splat}	path-matching-splat.js	Also matches / (splat is undefined)
Optional groups /:file{.:ext}	path-matching-optional.js	Braces for optional segments instead of ?
Regex chars in paths not supported	-	+, (), [], ? are treated as literals or throw

What's NOT yet implemented (left to do)

Express 5 feature	Status	Notes
res.sendFile() hidden/from options rejection	N/A	Options were never implemented in ultimate-express
router.param() rejects array of names	Not implemented	Edge case, requires a lot of changes
express.static.mime removed	Not implemented	Would need to remove the export
MIME type changes (.js → text/javascript)	Not implemented	Depends on mime-db version used
express:router debug namespace change	N/A	ultimate-express doesn't use debug module
res.render() enforced async	Not implemented	Current implementation may already be async depending on engine
Brotli decompression in body middleware	Already supported	Was implemented before this PR

Tests

Added 16 tests in tests/tests/v5/ with SKIP_V4 marker. Each test:

1. Is skipped for Express 4 comparison (uses SKIP_V4 marker)
2. Runs against native express@5 (via express5 package in devDependencies)
3. Runs against ultimate-express with version: 5

close #83

[dimdenGD]

For this to be merged, provide full list of changes and what's left to support Express 5. Also looking at your tests, it seems that you test against express and not express5 ("express5": "npm:express@5" in package.json). Every Expess 5 divergence should be tested.

[cesco69]

Thanks for the feedback. I've updated the PR. I also fixed two behaviors I got wrong in the first iteration.