Normalize repeated execpolicy path separators

[GreyforgeLabs]

Summary

• Collapse repeated forward slashes while normalizing execpolicy paths
• Normalize backslashes during the same pass before sensitive path checks
• Add regression tests for triple-slash sensitive paths and repeated separators

Validation

• cargo fmt --package cortex-execpolicy --check
• git diff --check
• cargo test -p cortex-execpolicy
• cargo check -p cortex-execpolicy

Addresses PlatformNetwork/bounty-challenge#53132.

[greptile-apps]

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