Make Presidio a required dependency

[steven10a]

• Made Presidio a required dep
• Updated docs and readme to reflect this
• Changed hello_world.py to use PII as a preflight instead of input

[Copilot]

Pull Request Overview

This PR makes Presidio a required dependency for the Guardrails library and updates the codebase to remove optional import handling. The changes streamline the dependency management by moving Presidio from an optional extra to a core requirement.

Key changes:

• Made presidio-analyzer a required dependency in pyproject.toml instead of an optional extra
• Removed TYPE_CHECKING imports and exception handling for missing Presidio packages
• Updated example configuration to use PII detection as a preflight check instead of input check

Reviewed Changes

Copilot reviewed 6 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/guardrails/checks/text/secret_keys.py	Removed optional Presidio import handling and moved imports to top level
src/guardrails/checks/text/pii.py	Removed TYPE_CHECKING imports and error handling for missing Presidio
pyproject.toml	Moved presidio-analyzer from optional "presidio" extra to required dependencies
examples/basic/hello_world.py	Changed PII detection from input to pre_flight guardrail
docs/quickstart.md	Removed optional Presidio installation instructions
README.md	Updated installation instructions to remove optional Presidio dependency

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[gabor-openai]

LGTM thank you!