Fix failing tests for markdown detection + Unskip passing tests

[vivganes]

This PR does 2 things:

1. Fix the failing (and currently skipped) unit test looksLikeCode - detects Markdown as non-code

• Any line that starts with # followed by a space is most probably a markdown.
• Except: C++ or C preprocessor directives like # include <stdio.h>
• Python comment is another case, but we cannot detect them deterministically.

2. Unskip already passing tests in codeGuesser.spec.ts

[Copilot]

Pull Request Overview

This PR fixes failing unit tests for markdown detection in the code guesser functionality and unskips previously passing tests. The changes improve the accuracy of distinguishing between markdown content and actual code.

• Fix markdown detection logic to properly identify markdown headers while preserving C/C++ preprocessor directive detection
• Unskip three previously passing tests that were disabled
• Add a new test case for C++ preprocessor directives to ensure they're still correctly identified as code

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
src/extension/prompt/common/codeGuesser.ts	Added markdown header detection logic with C/C++ preprocessor directive exception handling
src/extension/prompt/node/test/codeGuesser.spec.ts	Unskipped passing tests and added new test case for C++ preprocessor directives

[vivganes]

@ulugbekna I wanted to check if you got a chance to look at this PR