Add RawPacketBase as common base class between raw packet implementations.

[Dimi1010]

Part of #1899

This PR adds a class RawPacketBase that is to work as a common base class between RawPacket and MBufRawPacket.
The current iteration only takes over the management for timestamp and linkLayer as a minimal example, without defining common API yet.

The class is defined in the internal namespace while in development, with the eventual goal to be "published" to the main namespace when complete.

[codecov]

Codecov Report

❌ Patch coverage is 89.74359% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.88%. Comparing base (5b437d3) to head (985891c).

Files with missing lines	Patch %	Lines
Packet++/src/RawPacket.cpp	85.71%	3 Missing ⚠️
Packet++/header/RawPacket.h	94.44%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #1900      +/-   ##
==========================================
- Coverage   82.89%   82.88%   -0.01%     
==========================================
  Files         292      292              
  Lines       51834    51840       +6     
  Branches    11501    11316     -185     
==========================================
+ Hits        42966    42967       +1     
- Misses       7704     7710       +6     
+ Partials     1164     1163       -1     

Flag	Coverage Δ
alpine320	74.69% <80.95%> (-0.01%)	⬇️
fedora42	74.83% <80.95%> (-0.01%)	⬇️
macos-13	81.10% <89.65%> (-0.01%)	⬇️
macos-14	81.10% <89.65%> (-0.01%)	⬇️
macos-15	81.10% <89.65%> (-0.01%)	⬇️
mingw32	70.13% <55.00%> (-0.05%)	⬇️
mingw64	70.13% <55.00%> (-0.05%)	⬇️
rhel94	74.54% <80.95%> (-0.01%)	⬇️
ubuntu2004	58.84% <70.58%> (-0.03%)	⬇️
ubuntu2004-zstd	58.98% <70.58%> (+0.02%)	⬆️
ubuntu2204	74.47% <80.95%> (-0.01%)	⬇️
ubuntu2204-icpx	60.87% <89.65%> (-0.01%)	⬇️
ubuntu2404	74.72% <80.95%> (-0.01%)	⬇️
ubuntu2404-arm64	74.69% <80.95%> (-0.03%)	⬇️
unittest	82.88% <89.74%> (-0.01%)	⬇️
windows-2022	85.03% <93.54%> (-0.01%)	⬇️
windows-2025	85.05% <93.54%> (-0.01%)	⬇️
winpcap	85.05% <93.54%> (-0.01%)	⬇️
xdp	51.48% <71.42%> (-0.01%)	⬇️

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[tigercosmos]

LGTM