fix: update ELF parser tests to use existing test files

[VolodymyrBg]

Is this resolving a feature or a bug?

When I ran tests I bumped into this fail:

test elf::parser::tests::test_parse_elf_file_with_no_precompiles stdout ----
thread 'elf::parser::tests::test_parse_elf_file_with_no_precompiles' panicked at vm\src\elf\parser.rs:556:49:
called Result::unwrap() on an Err value: Os { code: 2, kind: NotFound, message: "The system cannot find the file specified." }
note: run with RUST_BACKTRACE=1 environment variable to display a backtrace

---- elf::parser::tests::test_parse_elf_file_with_precompile stdout ----
thread 'elf::parser::tests::test_parse_elf_file_with_precompile' panicked at vm\src\elf\parser.rs:523:49:
called Result::unwrap() on an Err value: Os { code: 2, kind: NotFound, message: "The system cannot find the file specified." }

---- elf::parser::tests::test_parse_elf_file_with_precompiles stdout ----
thread 'elf::parser::tests::test_parse_elf_file_with_precompiles' panicked at vm\src\elf\parser.rs:538:49:
called Result::unwrap() on an Err value: Os { code: 2, kind: NotFound, message: "The system cannot find the file specified." }

Describe your changes.

The tests in vm/src/elf/parser.rs were failing because they were looking
for non-existent test files. This commit updates the tests to use the
actual test files available in the project.

Tests previously failed with errors:
"Os { code: 2, kind: NotFound, message: "The system cannot find the file specified." }"

Modified test files:

• test_parse_elf_file_with_precompile
• test_parse_elf_file_with_precompiles
• test_parse_elf_file_with_no_precompiles

Also fixes unused variable warnings by prefixing variables with underscore.

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[VolodymyrBg]

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[sjudson]

Thanks for catching this, there is some ongoing internal work that should fix these tests more comprehensively, so I'm going to prioritize that approach (cc: @bhoberman).