gh-572: make multalm private

[Saransh-cpp]

Description

glass.fields.multalm is not used anywhere outside of the sampling function, so it should be private. This should not require deprecation as the function was never available in the documentation.

Closes: #572

Checks

• Is your code passing linting?
• Is your code passing tests?
• Have you added additional tests (if required)?
• Have you modified/extended the documentation (if required)?
• Have you added a one-liner changelog entry above (if required)?

[paddyroddy]

Examples test is failing

[paddyroddy]

Examples fixed!