Refactor ETag to use GZIP CRC32 trailer

[JosePineiro]

Refactor ETag generation to read CRC32 checksum from GZIP file trailer

• Changed _getEtag() signature to accept File handle instead of byte array
• Function now seeks to GZIP trailer and extracts CRC32 checksum
• Added error handling for file operations (seek/read failures)
• Returns boolean to indicate success/failure of ETag generation
• Maintains same hex conversion logic for consistent ETag format
• Simplifies code following DRY principle by eliminating duplicate read file

This refactoring maintains full backward compatibility

[Copilot]

Pull Request Overview

This PR refactors ETag generation for GZIP files to read the CRC32 checksum directly from the GZIP file trailer instead of requiring a separate byte array parameter. The refactor centralizes file operations within the _getEtag function and adds proper error handling while maintaining the same ETag format.

Key changes:

• Modified _getEtag() function signature to accept a File handle and return boolean success status
• Consolidated GZIP trailer reading logic into the _getEtag function with error handling
• Updated calling code to use the new function signature and handle return status

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/ESPAsyncWebServer.h	Updated _getEtag function signature to accept File parameter and return boolean
src/AsyncWebServerRequest.cpp	Refactored _getEtag implementation to handle file operations internally with error handling
src/WebResponses.cpp	Updated to use new _getEtag function and handle boolean return value

Comments suppressed due to low confidence (1)

[mathieucarbou]

@JosePineiro could you please rebase and fix the conflicts in this PR ? I will merge it after, thanks!

[JosePineiro]

@JosePineiro could you please rebase and fix the conflicts in this PR ? I will merge it after, thanks!

Please give me three days.

[mathieucarbou]

@JosePineiro : some conflicts still remain ;-)