[ENH] Add _log_pdf method to Uniform distribution

[Nadjoubiii]

• Implements mathematically exact log_pdf for uniform distribution
• Returns -log(b-a) for in-bounds points, -inf for out-of-bounds
• Eliminates numpy warnings from log(0) by using np.where
• Fulfills already-declared exact capability tag

Reference Issues/PRs

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[arnavk23]

There is already a pr for this i.e. #787. Please close this pr and try to look for issues under good first issue and enhancement which haven't been worked on before by contributors.