Remove direct qs dependency

[lukaselmer]

• As suggested here: Investigate replacing `qs` #5783 (comment)
• See also Dependency graph improvements (via npmgraph.js.org) #6647, Investigate replacing qs #5723, fix(deps): qs@^6.14.0 #6374, qs package security flaw #3230, qs module need to be update #3272, https://github.com/expressjs/express/pulls?q=is%3Apr+qs+is%3Aclosed
• This doesn't remove qs from body-parser

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[Copilot]

Pull Request Overview

This PR removes the built-in 'extended' query parser option from Express and moves the qs package from dependencies to devDependencies. Users must now provide a custom parser function to replicate the previous 'extended' behavior.

Key changes:

• Removed qs as a production dependency and added it as a devDependency
• Replaced the 'extended' query parser option with a helpful error message directing users to use a custom parser function
• Updated tests to use qs.parse directly instead of the deprecated 'extended' string option

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
package.json	Moved qs from dependencies to devDependencies
lib/utils.js	Removed qs import, removed parseExtendedQueryString function, and replaced 'extended' case with an error throw
test/req.query.js	Added qs import, updated tests to use qs.parse directly, and added test for new error behavior
History.md	Documented the breaking change with migration instructions

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