fix: coverage script reliability and cross-platform support

[mdqst]

fixed a few issues in the coverage script:

• replaced EXCLUDE="..." with an array EXCLUDES=(...) and used "${EXCLUDES[@]}" in lcov --remove, so patterns aren’t expanded by the shell.
• changed rm lcov.info && rm coverage.json to rm -f lcov.info coverage.json, preventing failures when coverage.json is missing.
• updated open coverage/foundry/index.html to check for xdg-open (Linux) and open (macOS), making it cross-platform.

this should make the script more robust and portable.

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PR-Codex overview

This PR updates the generate_coverage_report.sh script to improve the handling of excluded directories and enhance the file removal process, as well as the method for opening the coverage report in a cross-platform manner.

Detailed summary

• Changed EXCLUDE variable to an array EXCLUDES.
• Updated lcov command to use the array syntax for exclusions.
• Modified the rm command to use -f for forceful removal of files.
• Improved the method for opening the HTML report by checking for xdg-open or open commands.

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