Fix: Add type annotation and override PcapReader's __iter__ for mypy static type checking

[AbhishekPandey1998]

Summary

Fixes a mypy type-checking issue where PcapReader's __next__ method was inferred to return a tuple[bytes, PacketMetadata] instead of a Packet due to inheriting __iter__ declaration of RawPcapReader.

Changes

Overridden __iter__() method explicitly in PcapReader, with a type hint to indicate that PcapReader is an iterator over Packet objects.

Note: No test was added as no runtime behavior was changed.

fixes #4728

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.08%. Comparing base (b54fdb7) to head (43ba816).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4803      +/-   ##
==========================================
- Coverage   80.08%   80.08%   -0.01%     
==========================================
  Files         365      365              
  Lines       89027    89029       +2     
==========================================
  Hits        71296    71296              
- Misses      17731    17733       +2     

Files with missing lines	Coverage Δ
scapy/utils.py	73.90% <100.00%> (+0.02%)	⬆️

... and 2 files with indirect coverage changes

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