Functions error handling mechanism in acc2lin.R

Added validation checks for input parameters (accessions, ipg_file, assembly_path, lineagelookup_path).
Included error messages for missing or invalid inputs and file existence checks.
Wrapped main logic in tryCatch for graceful error handling during execution.
[x] Enhancement (adds functionality).

Checklist

[x] I have read and followed the CONTRIBUTING.md guidelines.
[x] I have searched for existing content to ensure this is not a duplicate.
[x] I have performed a self-review of these additions (including spelling, grammar, and related).
[x ] I have added comments to my code to help provide understanding.
[ ] I have added a test which covers the code changes found within this PR.
[x] I have deleted all non-relevant text in this pull request template. @jananiravi