Ship HeaderAwareGetHttpRequestAction in the package

[loevgaard]

Fixes gap G2 of #57.

Problem

payum/core's plain-PHP GetHttpRequest bridge never populates GetHttpRequest::$headers, and NotifyAction reads the QuickPay-Checksum-Sha256 header off exactly that property. So on a plain-PHP Payum every callback is rejected as unsigned (400) — silently, for every payment — unless the consumer found and copied the helper class hidden in examples/e2e/. That's a total failure of the notify path for a whole class of consumers, shipped as dev tooling.

Fix

• The action now lives in the package proper: Setono\Payum\Quickpay\Bridge\PlainPhp\Action\HeaderAwareGetHttpRequestAction, with the registration snippet (addCoreGatewayFactoryConfig(['payum.action.get_http_request' => …])) in its docblock and in docs/UPGRADE-2.0.md. It is not auto-registered: the core gateway factory already defines that key, so a default could never take effect, and force-setting it would stomp the Symfony bridge for Symfony/Sylius consumers who don't need this.
• Header values from getallheaders() (the SAPI's own or a polyfill — guzzle ships ralouphie/getallheaders, which passes $_SERVER values through untouched) and from the $_SERVER fallback are sanitized identically (string names, scalar values, everything else dropped), so the result is deterministic across SAPIs.
• The e2e harness uses the shipped class; its local copy is deleted.
• GetHttpRequest is declared a universalObjectCratesClass for PHPStan — headers is a dynamic property (payum marks the class #[AllowDynamicProperties]), and this is PHPStan's documented way to accept that contract.

The README section pointing plain-PHP consumers at this class comes in the follow-up docs PR, which is stacked on this one.

Tests

New HeaderAwareGetHttpRequestActionTest: headers populated alongside the parent's fields, the reconstructed checksum-header name is findable by NotifyAction's case-insensitive match, and non-header / non-scalar $_SERVER entries are dropped.

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.46%. Comparing base (6122f5f) to head (952142e).
⚠️ Report is 2 commits behind head on 2.x.

Files with missing lines	Patch %	Lines
...lainPhp/Action/HeaderAwareGetHttpRequestAction.php	66.66%	8 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                2.x      #64      +/-   ##
============================================
- Coverage     97.43%   95.46%   -1.97%     
- Complexity      126      138      +12     
============================================
  Files            14       15       +1     
  Lines           351      375      +24     
============================================
+ Hits            342      358      +16     
- Misses            9       17       +8     

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