version-bump 0.14.3

[amanjaiswal73892]

This pull request updates the BrowserGym repository from development version 0.14.3.dev4 to the stable release 0.14.3 across all packages and documentation. The main changes include version bumps in all relevant files to ensure consistency and proper dependency management.

Version updates across the codebase:

• Updated all requirements.txt files in submodules (such as assistantbench, experiments, miniwob, visualwebarena, webarena, webarenalite, and webarena_verified) to require browsergym-core==0.14.3 [1] [2] [3] [4] [5] [6] [7].
• Updated the package version and all internal dependencies in browsergym/pyproject.toml from 0.14.3.dev4 to 0.14.3 for all BrowserGym modules.
• Bumped the version string in browsergym/core/src/browsergym/core/__init__.py to 0.14.3.
• Updated the documentation version in docs/src/conf.py to 0.14.3.