fix: make cargo test testnet work on windows

[fdefelici]

Description

this patch makes cargo test testnet command work properly on windows.
Addressed:

• compilation issue due to usage of unix apis
• test runtime failure due to path naming not supported by windows

Applicable issues

• fixes [windows dev] test compilation fails due to unix apis #5930

Additional info (benefits, drawbacks, caveats)

Checklist

• Test coverage for new or modified code paths
• Changelog is updated
• Required documentation changes (e.g., docs/rpc/openapi.yaml and rpc-endpoints.md for v2 endpoints, event-dispatcher.md for new events)
• New clarity functions have corresponding PR in clarity-benchmarking repo
• New integration test(s) added to bitcoin-tests.yml