Fix error messages for invalid parameter names

[cmbant]

Fixes #469

Improve error messages when parameter names are not valid Python identifiers (e.g., al0_-1 containing a hyphen):

1. Sampled input params: Provide complete working example with derived: False
2. Input function params: Explain that derived: False is needed to prevent tracking as derived
3. Output params: Remove incorrect renames suggestion (doesn't actually work for output params), advise not requesting as derived instead

Example error messages after this change:

Sampled param with invalid name:

Parameter name 'al0_-1' is not a valid Python variable name...
If this is an input parameter of a likelihood or theory, whose name you cannot change, define an associated sampled one with a valid name:

  p_prime:
    prior: ...
  al0_-1:
    value: 'lambda p_prime: p_prime'
    derived: False

Output param with invalid name:

Parameter name 'al0_-1' is not a valid Python variable name...
If this is an output parameter of a likelihood or theory whose name you cannot change, do not request it as derived.

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Pull Request opened by Augment Code with guidance from the PR author