fix: ctx.assert() now throws errors that are instanceof HttpError

[mibragimov]

Problem

ctx.assert() was delegated entirely to the http-assert package, which bundles its own copy of http-errors ~1.8.0. Because koa depends on http-errors ^2.0.0, npm installs two separate versions with distinct class prototypes. As a result, errors thrown by ctx.assert() fail an instanceof HttpError check even though the errors look identical:

import { HttpError } from 'koa'

router.get('/test', async (ctx) => {
  try {
    ctx.assert(false, 401, 'Unauthorized')
  } catch (e) {
    console.log(e instanceof HttpError) // ❌ false — should be true
  }
})

Fixes #1925

Solution

Replace the http-assert dependency with an inline assert() helper inside lib/context.js that creates HTTP errors through the same createError function (from http-errors ^2.0.0) used by ctx.throw() and re-exported as koa.HttpError.

The full http-assert API is preserved:

• ctx.assert(value, status[, msg[, opts]])
• ctx.assert.equal / notEqual / strictEqual / notStrictEqual
• ctx.assert.deepEqual / notDeepEqual — now uses util.isDeepStrictEqual() (available since Node 9, koa requires Node ≥ 18)
• ctx.assert.fail / ok

After this fix

console.log(e instanceof HttpError) // ✅ true

Tests

Added a new test case in __tests__/context/assert.test.js that asserts the thrown error is instanceof HttpError. All 430 existing tests continue to pass.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.90%. Comparing base (d3ea8bf) to head (ec34662).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1937   +/-   ##
=======================================
  Coverage   99.90%   99.90%           
=======================================
  Files           9        9           
  Lines        2094     2141   +47     
=======================================
+ Hits         2092     2139   +47     
  Misses          2        2           

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