refactor: remove code duplication

[georgidhristov]

Summary

Small low-risk cleanup focused on reducing duplication and improving maintainability without changing behavior.

Changes

• Centralized header redaction logic into a shared utility used by incoming and outgoing HTTP capture.
• Removed duplicated capture-size calculation logic through a shared option property.
• Applied minor code cleanup and simplifications in utility methods.

Notes

• No functional changes intended.
• JSON compare/diff logic was intentionally left unchanged.
• Compare URL validation was intentionally left unchanged.
• Stream/body capture behavior was intentionally left unchanged.

Verification

• dotnet build passes with 0 warnings and 0 errors.