fix(algo): link networkit_state and deploy its DLL on Windows

[adsharma]

Problem

Windows link of the algo extension fails with LNK2019/LNK1120, e.g.:

networkit.lib(Log.cpp.obj) : error LNK2019: unresolved external symbol
  "__declspec(dllimport) enum Aux::Log::LogLevel __cdecl
  NetworKit::GlobalState::getLogLevel(void)" (__imp_?getLogLevel@GlobalState@NetworKit@@...)

Root cause

The vendored icebug Windows artifact splits NetworKit into two pieces:

• lib/networkit.lib — a large static lib (Log.cpp.obj, SignalHandling.cpp.obj, ...)
• lib/networkit/networkit_state.lib + networkit_state.dll — the GlobalState singleton

The static lib's members reference the GlobalState accessors via __imp_* dllimport
thunks (21 of them), but the algo extension only linked networkit.lib — never
networkit_state.lib — so the __imp_GlobalState::* thunks were unresolved.

Verified against the actual artifact: networkit.lib defines zero __imp_ symbols but
references 21 __imp_GlobalState::*; networkit_state.lib defines both the plain and
__imp_ forms of all 24 GlobalState accessors.

Fix

• download_icebug.cmake: on WIN32, also find_library networkit_state (in both the
  prebuilt vendor/lib/networkit path and the ICEBUG_SOURCE_DIR local-build path) and set
  ICEBUG_STATE_LIB / ICEBUG_STATE_DLL.
• algo/CMakeLists.txt: on WIN32, link ICEBUG_STATE_LIB and add a post-build copy of
  networkit_state.dll next to the built extension so the imports resolve at load time.

Notes

• Non-Windows is unaffected (the networit state is bundled into the shared lib).
• If networkit_state.dll still isn't found at load time on Windows (it must be on PATH or
  beside the loading module), the extension may fail to load even though linking now succeeds —
  the post-build copy places it next to libalgo.lbug_extension.

[adsharma]

Landed via #52