ECC-2142: Use RAII LockGuard and thread-safe hashmap in BufrElementsTable

[joobog]

Description

In this PR

• The C++ mutex classes replace the corresponding MUTEX macros
• A LockGuard class makes memory management safer by using RAII
• The grib_trie data structure in BufrElementsTable is replaced with a thread-safe hashmap

JIRA: https://jira.ecmwf.int/browse/ECC-2142

Contributor Declaration

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• All authors agree to the Contributor License Agreement.
• The code follows the project's coding standards.
• I have performed self-review and added comments where needed.
• I have added or updated tests to verify that my changes are effective and functional.
• I have run all existing tests and confirmed they pass.