#20 feat/ns http

Implement memory-safe synchronous HTTP client

Introduces the ns_http module, wrapping Rust's reqwest crate to provide
a modern, synchronous HTTP API to C without the complexity and callback
management of libcurl.

Key additions:

• Implemented ns_http_get and ns_http_post for standard web requests.
• Added ns_http_response struct to cleanly capture HTTP status codes and
  pack the response body directly into memory-safe SSO ns_string structs.
• Introduced the ns_autohttp macro, leveraging the GCC/Clang cleanup
  attribute to provide RAII, automatically freeing HTTP response buffers
  when they fall out of scope.
• Created 18_http.c example demonstrating fetching
  data and pushing JSON payloads.
• Registered ns_http crate in the workspace and added reqwest dependency.

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Summary by cubic

Adds a new ns_http module with a simple, memory-safe synchronous HTTP client for C. Supports GET/POST with RAII cleanup; POST is binary‑safe and GET/POST now share a unified client configuration.

• New Features

  • New ns_http crate using blocking reqwest with a browser-like User-Agent.
  • ns_http_get and ns_http_post; results via ns_http_response (status + ns_string body).
  • ns_autohttp macro for auto-free; header include/ns_http.h; example examples/18_http.c; Makefile links -lns_http.

• Bug Fixes

  • POST: binary-safe payloads (raw bytes) and null payloads return NsError::InvalidInput.
  • GET: response decoding errors now return generic NsError::Any.
  • Centralized client configuration to prevent drift between GET and POST.
  • Makefile uninstall uses LIBS_TO_INSTALL to remove all installed libs.