Fix build_and_run_tests.sh command error.

[tsogoo]

First, kudos to the OpenSpiel team for maintaining such an impressive and valuable framework for reinforcement learning and game theory research!

This PR addresses an issue with the pybind11 dependency in OpenSpiel, stemming from the smart_holder branch being archived and renamed to archive/smart_holder in the pybind11 repository (see: https://github.com/pybind/pybind11/tree/archive/smart_holder). The original build process attempted to clone the now-deprecated smart_holder branch, causing errors.

Changes Made

1. Updated pybind11 Branch: Modified the cached_clone command in ./open_spiel/scripts/build_and_run_tests.sh to use the master branch of pybind11 instead of smart_holder or archive/smart_holder. The smart_holder features are now fully integrated into master, making this the appropriate target.
2. Removed Deprecated Code: As per the pybind11 migration guidelines, removed the obsolete #include <pybind11/smart_holder.h> and the following deprecated macros from the codebase:
   • PYBIND11_SMART_HOLDER_TYPE_CASTERS
     These are no longer needed with the latest pybind11.

Result

These changes resolve the build errors encountered when running ./open_spiel/scripts/build_and_run_tests.sh, ensuring compatibility with the current pybind11 master branch.

Please review and let me know if additional adjustments are needed!

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[tsogoo]

I realized another PR #1318 that fixes the error. so i closed.

[lanctot]

Oh, wow, wonderful. Thanks for this!

[lanctot]

(Yes I've been chatting with @rwgk from the pybind11 team who has been looking at fixing this in a similar way -- but thank you for fixing this nonetheless.)

[lanctot]

Opened a new version now (#1320) based on a unification of this with #1318