Expose header parsing error variables

[ReneWerner87]

Summary

• expose exported error variables for header parsing to replace inline error constructions
• update header parsing logic and related utilities to rely on the exported errors
• adjust server tests to reference the new exported error values

[Copilot]

Pull Request Overview

This PR refactors internal error variables to exported error variables, making them part of the public API. This allows API consumers to perform error checking and matching against specific error conditions.

• All internal error variables (errNeedMore, errSmallBuffer, errNonNumericChars) are converted to exported versions with PascalCase naming
• Multiple new exported error variables are introduced for various parsing and validation scenarios
• All references throughout the codebase are updated to use the new exported error names

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
header.go	Consolidates all error variable declarations into a single exported var block; updates all internal references to use new exported error names
headerscanner.go	Updates error assignment to use exported ErrNeedMore
server.go	Updates error comparison to use exported ErrNeedMore
server_test.go	Updates test to use exported ErrSmallReadBuffer

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[gaby]

👍 for this

[erikdubbelboer]

Thanks!

[ReneWerner87]

Just wanted to prevent such situations, not that you change the error messages and we are then outdated.

https://github.com/gofiber/fiber/blob/19cc3f56f09fa758fc6863c67c3747d6639029c2/app.go#L1327