Part of kcenon/common_system#454

What

Update the compiler requirements in README.md to reflect that network_system transitively requires GCC 13+/Clang 17+ through its thread_system dependency.

• Current: README documents GCC 11+/Clang 14+ as minimum compiler requirement
• Expected: README documents GCC 13+/Clang 17+ with a note explaining the transitive dependency
• Scope: README.md compiler requirements section only

Why

• network_system requires thread_system as a core dependency
• thread_system requires GCC 13+/Clang 17+ (higher than the ecosystem baseline of GCC 11+/Clang 14+)
• Users attempting to build network_system with GCC 11/12 will encounter cryptic template or concept errors from thread_system headers
• Accurate documentation prevents wasted debugging time

Where

• README.md — Requirements/Prerequisites section listing compiler versions

How

Technical Approach

Update the compiler version row in the requirements table:

| C++20 Compiler | GCC **13+** / Clang **17+** / MSVC 2022+ / Apple Clang 14+ | Yes |

Add explanatory note:

> **Note**: Compiler requirements are higher than some other ecosystem systems due to the thread_system dependency (GCC 13+/Clang 17+). See [thread_system requirements](https://github.com/kcenon/thread_system#requirements) for details.

Acceptance Criteria

• README lists GCC 13+ and Clang 17+ as minimum requirements
• Note explains the reason (thread_system transitive dependency)
• Consistent with actual build requirements