Unify the 5 duplicated HTTP clients

[ff225]

Priority: High

There are 5 near-identical HTTP client files (~4,500 duplicated lines). A fix in one must be manually replicated in the others, which is a concrete regression risk.

File	Variant
http_client.py	static image
http_clientCAMlaptop.py	laptop webcam
http_clientCAMlaptopBench.py	laptop webcam + benchmark
http_clientCAMpi.py	Raspberry Pi camera
http_clientCAMpiBench.py	Raspberry Pi + benchmark

Tasks

• Extract a base SCIoTClient
• Strategy pattern for the image source (static / webcam / picamera)
• Benchmark as a flag/mixin instead of separate files

Files

• src/client/python/http_client*.py

From the Feature 042 codebase review (recommendation #3).