mdbx: release v0.10.4

Acknowledgements:
-----------------
 - [Artem Vorotnikov](https://github.com/vorot93) for support [Rust wrapper](https://github.com/vorot93/mdbx-rs).
 - [Andrew Ashikhmin](https://github.com/yperbasis) for contributing to C++ API.

Fixes:
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 - Fixed possibility of looping update GC during transaction commit (no public issue since the problem was discovered inside [Positive Technologies](https://www.ptsecurity.ru).
 - Fixed `#pragma pack` to avoid provoking some compilers to generate code with [unaligned access](https://github.com/erthink/libmdbx/issues/235).
 - Fixed `noexcept` for potentially throwing `txn::put()` of C++ API.

Minors:
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 - Added stochastic test script for checking small transactions cases.
 - Removed extra transaction commit/restart inside test framework.
 - In debugging builds fixed a too small (single page) by default DB shrink threshold.


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