Benchmark for C++ PDQ Hasher

[16BitNarwhal]

Summary

Resolve #1696

C++ benchmark program for PDQ hashing
Benchmark implementation located in pdq/cpp/bin/benchmark-photo-hasher.cpp
Benchmark results in pdq/cpp/hashing/README.md

To run:

cd pdq/cpp
make bin/benchmark-photo-hasher
./benchmark-photo-hasher

Sample results (ran on Ubuntu 24.04.1 LTS, Intel Core i7-14700KF with 20 cores, 28 threads, 64GB RAM):

$ ./benchmark-photo-hasher ../data/reg-test-input/dih/
PHOTO COUNT:               8
ERROR COUNT:               0
TIME SPENT HASHING PHOTOS (SECONDS):     0.015171
PHOTOS HASHED PER SECOND:   527.324158
TIME SPENT READING PHOTOS (SECONDS):        0.299410
PHOTOS READ PER SECOND:     26.719229

[Dcallies]

Only minor comments, overall looks good. Nice find reusing existing functions in hashio

blocking q: Why did you delete b.jpg?

[Dcallies]

Thanks again for updating the readme!