Add Windows/MSVC support

[TuxedoFish]

Summary

Gets hyperliquid-sdk-cpp building and passing its full test suite on Windows/MSVC - the last blocker called out for eventually submitting this SDK as an official vcpkg port (vcpkg's port-acceptance CI builds across Windows/Linux/macOS by default).

Fixes needed, found by iterating against real windows-latest/MSVC CI:

• timegm: POSIX/glibc extension, no MSVC equivalent by that name - added an _mkgmtime/timegm split in ResponseTypes.h::parseOutcomeExpiry (same semantics), plus the <ctime> include it was transitively relying on before.
• /bigobj: Boost.Asio/Beast's heavy template instantiation blew past MSVC's default COFF object section-table limit (C1128) in WebsocketRunner.cpp.
• /EHsc: MSVC needs the exception model spelled out explicitly; this codebase throws/catches throughout.
• NOMINMAX / WIN32_LEAN_AND_MEAN / _WIN32_WINNT=0x0A00: standard guards against Boost.Asio's transitive <windows.h> (min/max macro collisions, header bloat, Asio's own "guessing the target Windows version" warning).
• ws2_32 / mswsock: Winsock link libraries Asio's networking code needs on Windows, not required on Linux/macOS.
• CI portability: ci.yml's build-and-test job now sets shell: bash at the job level (Git Bash is present on windows-latest, so the existing bootstrap-vcpkg.sh/mkdir -p steps run unmodified across all four OS/compiler combinations), and Build/Test use --config Release/-C Release (no-ops on Linux/macOS's single-config generator, required for Windows' multi-config Visual Studio generator).

Removed the stale "Windows/MSVC is intentionally out of scope" comment and the temporary branch-scoped windows-experiment.yml used to iterate against real MSVC without waiting on the full Linux/macOS/sanitizer/coverage suite each round.

Stacked on #160 (secp256k1 overlay-port removal) since both are prerequisites for a future vcpkg port submission.

Test plan

• Windows CI (windows-latest, MSVC): 100% passed, 29/29 tests (verified on this branch before folding into ci.yml's real matrix)
• Local Linux rebuild + ctest: 29/29 passing, confirming the if(WIN32)/if(MSVC)-guarded CMake changes don't affect non-Windows builds

🤖 Generated with Claude Code

https://claude.ai/code/session_018Le73N2EZjGLsCqmCScAse

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.09%. Comparing base (ee37310) to head (b519bfd).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #161   +/-   ##
=======================================
  Coverage   70.09%   70.09%           
=======================================
  Files          54       54           
  Lines        8840     8840           
  Branches      530      530           
=======================================
  Hits         6196     6196           
  Misses       2639     2639           
  Partials        5        5           

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