Implement bayesian update on task estimated duration to learn to plan better.

When the user sets the estimated duration, use the previous estimated durations, compare those to the actual measured durations in timewarrior, and update the new estimated duration accordingly using a bayesian update https://arxiv.org/pdf/0901.1342.pdf.

(Also if automatic scheduling is implemented, give warning if user appears to not be able to make task deadline #7 .)

The issue names no files, tests, or entry points. Start by identifying how estimated durations are set and how actual durations are obtained from Timewarrior, then review the linked Bayesian-update paper and define the completion criteria before implementing.

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