Remove UB std:: declarations

[chhwang]

Remove custom delcarations inside std:: of which behaviors are undefined by the standard

[Copilot]

Pull request overview

This PR removes undefined behavior by eliminating custom declarations inside the std:: namespace, which violates the C++ standard. The changes refactor std::to_string overloads to operator<< overloads and consolidate hash combining functionality into a centralized utility.

Key changes:

• Introduced mscclpp::detail::hashCombine utility function to replace duplicate std::hash_combine implementations
• Replaced std::to_string function declarations with operator<< overloads in the mscclpp namespace
• Removed std::hash<TransportFlags> forward declaration (no longer needed)

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
include/mscclpp/utils.hpp	Added hashCombine function in mscclpp::detail namespace with proper documentation
include/mscclpp/core.hpp	Replaced std::to_string declarations with operator<< overload declarations in mscclpp namespace, removed std::hash<TransportFlags> forward declaration
src/core.cc	Implemented operator<< overloads for Transport, DeviceType, and Device types
src/context.cc	Updated to use operator<< instead of std::to_string for Transport types
python/csrc/core_py.cpp	Updated Python binding to use stringstream with operator<< instead of std::to_string
src/include/execution_plan.hpp	Replaced inline hash_combine calls with mscclpp::detail::hashCombine in hash specializations
src/executor/executor.cc	Removed local hash_combine implementation, replaced with mscclpp::detail::hashCombine
include/mscclpp/algorithm.hpp	Removed local hash_combine implementation, replaced with mscclpp::detail::hashCombine

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