Fix cookie case sensitive name

[rajwinder-dev]

Summary

Preserve cookie name casing during cookie parsing.

Cookie attribute keys are still normalized to lowercase
(case-insensitive), but cookie names should remain
case-sensitive.

Changes

• Preserve original casing for cookie names
• Continue lowercasing cookie option keys
• Add test coverage for mixed-case cookie names

Reason

Cookie names are case-sensitive, but the parser was
lowercasing all keys including the cookie name.

Resolves #879

Checklist

• I have ensured my pull request is not behind the main or master branch of the original repository.
• I have rebased all commits where necessary so that reviewing this pull request can be done without having to merge it first.
• I have written a commit message that passes commitlint linting.
• I have ensured that my code changes pass linting tests.
• I have ensured that my code changes pass unit tests.
• I have described my pull request and the reasons for code changes along with context if necessary.