Fix markdown syntax errors and document repeat parameter in Ensembles.md

[ChrisRackauckas-Claude]

Summary

This PR fixes the markdown syntax errors in the "Parallel Ensemble Simulations Interface" documentation section that were making the documentation difficult to read, and adds missing documentation for the repeat parameter in prob_func.

Changes Made

• Fixed markdown syntax errors: Changed incorrect docs to @docs syntax in the "Full Timeseries Statistics" section (lines 111 and 154)
• Added missing closing backticks: Properly closed the @docs code block that was missing its closing backticks
• Documented the repeat parameter: Added comprehensive documentation for the repeat parameter in the prob_func signature, explaining that it tracks iteration numbers for reruns when output_func returns rerun=true

Details

The issue reported that the documentation starting from the "Full Timeseries Statistics" section had markdown syntax errors making it hard to read. Upon investigation, I found:

1. Two instances where docs was used instead of @docs in code blocks
2. A missing closing backtick sequence for an @docs block
3. The repeat parameter in prob_func was never explained in the documentation, even though it appears in all the examples

The repeat parameter documentation was added based on the comprehensive docstring in src/ensemble/ensemble_problems.jl which explains that repeat is the iteration of the repeat that starts at 1 and increments if rerun was true.

Test plan

• Verified all markdown syntax errors are fixed
• Confirmed the repeat parameter is now properly documented
• Ensured documentation maintains consistency with existing style

Fixes #1141

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