fix(tools): Use exec.LookPath to find bash executable before running bash commands

[ruinshe]

Fixes #228

Find the bash executable using exec.LookPath instead of hardcoding /bin/bash. Falls back to /bin/bash if not found in PATH. Improves compatibility on systems where bash might be installed in a non-standard location.

On some systems (e.g. NixOS), executables might not be in standard locations like /bin/bash.

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[ruinshe]

Currently I modified the bashBin in bash_tool.go in init function directly, if you think it's not a good choice and prefer passing the bash command path using parameters, or using other ways, please that me know.

[droot]

Currently I modified the bashBin in bash_tool.go in init function directly, if you think it's not a good choice and prefer passing the bash command path using parameters, or using other ways, please that me know.

Would prefer to keep init() side-effect free, suggested to move it closer to command construction. and its okay to duplicate code if needed.

[droot]

Thanks @ruinshe you will need to rebase the PR because we had to update the presubmits, sorry :(

[ruinshe]

Thanks @ruinshe you will need to rebase the PR because we had to update the presubmits, sorry :(

done