Add an uppercase hash option

Level: Beginner · Suggested labels: good first issue, enhancement

What to build

Hash Generator returns lowercase hexadecimal text. Add an optional
uppercase: bool = False parameter to return uppercase when requested.

Where to work

• Function: hash_text in src/mcp_tools_lab/tools/hashing.py
• Tests: tests/test_hashing.py
• Documentation: docs/tool-guide.md

Example

hash_text("abc", uppercase=True) should return a digest starting with BA7816BF.
hash_text("abc") should still start with ba7816bf.

Acceptance checklist

• Add the optional typed parameter without changing the default behavior.
• Uppercase changes only the digest string, not the algorithm name.
• Support all three existing algorithms.
• Test default output, uppercase output, and empty text.
• Update the docstring and guide with one example.

Hint: Python strings have an .upper() method. Calculate the digest once,
then choose whether to convert it.

Run python -m pytest tests/test_hashing.py -q, then python -m pytest -q.