Add remediation guidance for unpinned pip installs

[D9mond]

What kind of change does this PR introduce?

Feature improvement (adds remediation guidance for pip installs).

• PR title follows the guidelines defined in our pull request documentation

What is the current behavior?

Unpinned pip install commands are detected by the Pinned-Dependencies check,
but no remediation guidance is provided to users.

What is the new behavior (if this is a feature change)?

When an unpinned pip install command is detected, the result now includes
a remediation message suggesting:

• Using --require-hashes
• Using hashed lockfiles
• Generating hashed requirements with pip-tools
• Following pip secure install best practices
• Tests for the changes have been added (for bug fixes/features)

Which issue(s) this PR fixes

NONE

Special notes for your reviewer

This change mirrors the remediation pattern already implemented for NuGet,
providing more actionable guidance for Python users.

Does this PR introduce a user-facing change?

Adds remediation guidance for unpinned pip install commands in the
Pinned-Dependencies check output.
For user-facing changes, please add a concise, human-readable release note to
the release-note

(In particular, describe what changes users might need to make in their
application as a result of this pull request.)

Adds remediation guidance for unpinned pip install commands in the
Pinned-Dependencies check output.