[ENH] zero-inflated distribution

[Khushmagrawal]

Reference Issues/PRs

Partially fixes #554

What does this implement/fix? Explain your changes.

Adds support for Zero-inflated distribution

Does your contribution introduce a new dependency? If yes, which one?

No.

What should a reviewer concentrate their feedback on?

• Correctness of the implementation
• Design decision of making the lower bound inclusive in truncated.py

Did you add any tests for the change?

No

Any other comments?

After the ZeroInflated implementation is reviewed, I plan to add ZeroInflatedPoisson and ZeroInflatedNegativeBinomial as well using _DelegatedDistribution

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For new estimators

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[Khushmagrawal]

Fixed the off-by-one errors causing test_ppf_and_cdf to fail. The issue was due to floating-point error when q_rescaled is divided by p. Resolved by subtracting a small epsilon from q_rescaled (similar to #568).
The workflow passes on my fork with this change