[200_26] 将 (scheme file) 相关代码从 s7.c 迁移到 s7_scheme_file.c

[da-liii]

• 移除 s7.c 中 delete-file 的实现（已经通过 tbox 重新实现了）
• file-exists?在 s7.c 中的相关函数已经移除，可能需要清理一下 s7.c
• 剩余函数的迁移
• tests/goldfish/scheme/file-test.scm 的测试用例补充和文档补充

[aadiexii]

Hi @da-liii , I'd like to work on this issue. I'll handle all four sub-tasks —-removing delete-file from
s7.c, cleaning up file-exists leftovers, migrating the remaining file functions to s7_scheme_file.c, and adding supplementary test cases and documentation to file-test.scm.
I'll test everything locally and raise a PR with screenshots of successful compilation and tests. Should I go ahead?