Treat warnings as errors, move third-party stuff out of warning checks

[alan-george-lk]

This PR does the following:

• Compiler warnings are now treated as errors (intentionally not fixed due to removal soon)
• Warnings from third-party code are no longer visible in build output/checked
• Minor fixes to code that flagged warnings

Testing

Tested locally. Significantly cleans up compiler output; only the bridge shows warnings now. Warnings from protobuf, abseil, etc are gone:

==> Building (Release) with 18 parallel jobs...
[1/30] Building CXX object bridge/CMakeFiles/livekit_bridge.dir/src/livekit_bridge.cpp.o
/Users/alan.george/LiveKit/client-sdk-cpp/bridge/src/livekit_bridge.cpp:303:18: warning: exception of type 'const std::runtime_error &' will be caught by earlier handler [-Wexceptions]
  303 |   } catch (const std::runtime_error &e) {
      |                  ^
/Users/alan.george/LiveKit/client-sdk-cpp/bridge/src/livekit_bridge.cpp:300:18: note: for type 'const std::exception &'
  300 |   } catch (const std::exception &e) {
      |                  ^
/Users/alan.george/LiveKit/client-sdk-cpp/bridge/src/livekit_bridge.cpp:306:18: warning: exception of type 'const livekit::RpcError &' will be caught by earlier handler [-Wexceptions]
  306 |   } catch (const livekit::RpcError &e) {
      |                  ^
/Users/alan.george/LiveKit/client-sdk-cpp/bridge/src/livekit_bridge.cpp:303:18: note: for type 'const std::runtime_error &'
  303 |   } catch (const std::runtime_error &e) {
      |                  ^
/Users/alan.george/LiveKit/client-sdk-cpp/bridge/src/livekit_bridge.cpp:325:18: warning: exception of type 'const std::runtime_error &' will be caught by earlier handler [-Wexceptions]
  325 |   } catch (const std::runtime_error &e) {
      |                  ^
/Users/alan.george/LiveKit/client-sdk-cpp/bridge/src/livekit_bridge.cpp:322:18: note: for type 'const std::exception &'
  322 |   } catch (const std::exception &e) {
      |                  ^
/Users/alan.george/LiveKit/client-sdk-cpp/bridge/src/livekit_bridge.cpp:328:18: warning: exception of type 'const livekit::RpcError &' will be caught by earlier handler [-Wexceptions]
  328 |   } catch (const livekit::RpcError &e) {
      |                  ^
/Users/alan.george/LiveKit/client-sdk-cpp/bridge/src/livekit_bridge.cpp:325:18: note: for type 'const std::runtime_error &'
  325 |   } catch (const std::runtime_error &e) {
      |                  ^
/Users/alan.george/LiveKit/client-sdk-cpp/bridge/src/livekit_bridge.cpp:344:18: warning: exception of type 'const std::runtime_error &' will be caught by earlier handler [-Wexceptions]
  344 |   } catch (const std::runtime_error &e) {
      |                  ^
/Users/alan.george/LiveKit/client-sdk-cpp/bridge/src/livekit_bridge.cpp:341:18: note: for type 'const std::exception &'
  341 |   } catch (const std::exception &e) {
      |                  ^
/Users/alan.george/LiveKit/client-sdk-cpp/bridge/src/livekit_bridge.cpp:347:18: warning: exception of type 'const livekit::RpcError &' will be caught by earlier handler [-Wexceptions]
  347 |   } catch (const livekit::RpcError &e) {
      |                  ^
/Users/alan.george/LiveKit/client-sdk-cpp/bridge/src/livekit_bridge.cpp:344:18: note: for type 'const std::runtime_error &'
  344 |   } catch (const std::runtime_error &e) {
      |                  ^
/Users/alan.george/LiveKit/client-sdk-cpp/bridge/src/livekit_bridge.cpp:364:18: warning: exception of type 'const std::runtime_error &' will be caught by earlier handler [-Wexceptions]
  364 |   } catch (const std::runtime_error &e) {
      |                  ^
/Users/alan.george/LiveKit/client-sdk-cpp/bridge/src/livekit_bridge.cpp:361:18: note: for type 'const std::exception &'
  361 |   } catch (const std::exception &e) {
      |                  ^
/Users/alan.george/LiveKit/client-sdk-cpp/bridge/src/livekit_bridge.cpp:367:18: warning: exception of type 'const livekit::RpcError &' will be caught by earlier handler [-Wexceptions]
  367 |   } catch (const livekit::RpcError &e) {
      |                  ^
/Users/alan.george/LiveKit/client-sdk-cpp/bridge/src/livekit_bridge.cpp:364:18: note: for type 'const std::runtime_error &'
  364 |   } catch (const std::runtime_error &e) {
      |                  ^
/Users/alan.george/LiveKit/client-sdk-cpp/bridge/src/livekit_bridge.cpp:384:18: warning: exception of type 'const std::runtime_error &' will be caught by earlier handler [-Wexceptions]
  384 |   } catch (const std::runtime_error &e) {
      |                  ^
/Users/alan.george/LiveKit/client-sdk-cpp/bridge/src/livekit_bridge.cpp:381:18: note: for type 'const std::exception &'
  381 |   } catch (const std::exception &e) {
      |                  ^
/Users/alan.george/LiveKit/client-sdk-cpp/bridge/src/livekit_bridge.cpp:387:18: warning: exception of type 'const livekit::RpcError &' will be caught by earlier handler [-Wexceptions]
  387 |   } catch (const livekit::RpcError &e) {
      |                  ^
/Users/alan.george/LiveKit/client-sdk-cpp/bridge/src/livekit_bridge.cpp:384:18: note: for type 'const std::runtime_error &'
  384 |   } catch (const std::runtime_error &e) {
      |                  ^
10 warnings generated.
[30/30] Linking CXX executable bin/livekit_integration_tests; Copying dylibs to integration test directory