lseek_syscall and close_syscall updates (#311)

* Added comments for lseek syscall

* Added tests for lseek syscall

* Added comments for close_syscall

* Added tests for close syscall

* Addressed review comments

* Addressed review comments

* Addressed review comment

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Co-authored-by: Nicholas Renner <nicholassrenner@gmail.com>

Author: namanlalitnyu