Cleanup of PcapLiveDevice capture machinery.

[Dimi1010]

This PR moves the implementation of the capture procedures to internally linked functions in PcapLiveDevice.cpp and aims to reduce the the need for extensive bookkeeping of capture thread only variables inside the device object's fields.

The static member function callback routines for pcap_dispatch have been replaced with internal linkage free functions to improve readability and encapsulation. The user token is now expected to be a pointer to a specific capture context object instead of the device instance.

Replacement list:

• onPacketArrivesCallback replaces onPacketArrives. Expects user token of type CaptureContext
• onPacketArrivesAccumulator replaces onPacketArrivesNoCallback. Expects user token of type AccumulatorCaptureContext
• onPacketArrivesCallbackWithCancellation replaces onPacketArrivesBlockingMode. Expects user token of type CaptureContextST
• Added new callback handler onPacketArrivesNoop to be used when no handling is required.

Replaced captureThreadMain static private function with internal linkage free functions. The free functions take their inputs as parameters instead of relying on data from the implicit this pointer, simplifying data ownership and reducing risk of data races.

• captureThreadMain - used for callback or noop capture.
• captureThreadMainAccumulator - used for accumulating the packets into a RawPacketVector.

Changed blocking mode capture to utilize onPacketArrivesCallbackWithCancellation. The new infrastructure provides a layer of separation between the device threading machinery and the cancellation requests by relying on requestStop flag to record a cancellation request that is then forwarded to m_StopThread after dispatch finishes instead of directly writing to m_StopThread.

Removed PcapLiveDevice member fields previously only used to store data for the capture thread as that data is now stored in context objects created on demand during capture startup.

[codecov]

Codecov Report

Attention: Patch coverage is 67.06587% with 55 lines in your changes missing coverage. Please review.

Project coverage is 83.12%. Comparing base (e9ad86c) to head (32fb349).

Files with missing lines	Patch %	Lines
Pcap++/src/PcapLiveDevice.cpp	67.06%	36 Missing and 19 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #1838      +/-   ##
==========================================
- Coverage   83.18%   83.12%   -0.06%     
==========================================
  Files         285      285              
  Lines       49843    49888      +45     
  Branches    10589    10835     +246     
==========================================
+ Hits        41461    41470       +9     
+ Misses       7575     7277     -298     
- Partials      807     1141     +334     

Flag	Coverage Δ
alpine320	75.40% <50.92%> (-0.07%)	⬇️
fedora42	75.50% <51.37%> (-0.07%)	⬇️
macos-13	80.66% <63.76%> (-0.04%)	⬇️
macos-14	80.66% <63.76%> (-0.04%)	⬇️
macos-15	80.65% <63.76%> (-0.04%)	⬇️
mingw32	71.44% <46.72%> (-0.13%)	⬇️
mingw64	71.41% <43.92%> (-0.15%)	⬇️
npcap	84.99% <65.04%> (-0.13%)	⬇️
rhel94	75.28% <50.92%> (-0.10%)	⬇️
ubuntu2004	59.17% <54.54%> (+<0.01%)	⬆️
ubuntu2004-zstd	59.28% <54.54%> (-0.03%)	⬇️
ubuntu2204	75.20% <50.92%> (-0.07%)	⬇️
ubuntu2204-icpx	61.42% <51.44%> (-0.11%)	⬇️
ubuntu2404	75.43% <50.92%> (-0.10%)	⬇️
ubuntu2404-arm64	75.44% <50.92%> (-0.07%)	⬇️
unittest	83.12% <67.06%> (-0.06%)	⬇️
windows-2022	84.90% <62.60%> (-0.21%)	⬇️
windows-2025	85.03% <65.04%> (-0.13%)	⬇️
winpcap	85.14% <60.86%> (-0.13%)	⬇️
xdp	51.35% <0.00%> (-0.06%)	⬇️

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[Dimi1010]

Can we review this? It has been sitting here for a while.

[tigercosmos]

@Dimi1010 It's a big one... That's why... I will look into this recently.