[Data migration script] Misc improvements

[ouvreboite]

Incremental improvements of the migration notebook:

• handle unknown observation types (tools/agent/...) as span
• ensure that traces related to a migrated dataset run are migrated (even if the trace migration has been skipped)
• make the trace migration idempotent: if the trace is already present in the destination (i.e. same trace id), it is skipped
• use the from/to date params during the dataset run migration: this allows to only migrat recent dataset runs
• ensure the relative ordering of the dataset runs is kept: the createdAt are still changed, but at least their relative order is consistent
• keep the observation and score ids instead of recreating new random ones
• url encode the run names manually when calling GET /api/public/datasets/{datasetName}/runs/{runName}, mitigating [Python] Path parameters are not url encoded fern-api/fern#13065 while it is fixed

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[ouvreboite]

Force pushed to use my github account as author