Add parameter domain checks to analytical integrals

[swetank18]

Depends on #20992

Motivation:
Several analytical integrals assume valid parameter domains (e.g. sigma > 0)
without enforcing them, which may lead to undefined numerical behavior.

Changes:

• Add explicit parameter-domain checks for Gaussian, Landau, and Crystal Ball integrals
• Return QuietNaN for invalid parameter configurations

Impact:

• Improves robustness and predictability of analytical integrations
• No API changes