Lower default threshold for skipped failed choices to 0.1%

[i-am-sijia]

This pull request tightens the default allowed threshold for failed choices and clarifies documentation around the transition to skip_failed_choices.

• It lowers the default fraction_of_failed_choices_allowed from 0.1 to 0.001, as discussed in Default setting for skipping households on simulation failure #1052 (comment), causing the model to fail with far fewer skipped households, and
• Updates the user guide to explain the new behavior, including expected warnings and potential crashes when agencies run their existing model with this new feature for the first time.

Impact on existing model runs:
With skip_failed_choices defaulted to True and an allowed failure threshold as low as 0.1%, failures that were previously silently masked will now generate warnings, be explicitly skipped, and counted toward the threshold. As a result, model runs that previously completed "successfully" may now fail earlier, surfacing underlying specification or data issues that require attention rather than being silently absorbed. @jpn-- we may want to include this note in the next ActivitySim release note.

[jpn--]

LGTM.

The place to put the notice for users so that it appears in the next release notes is here. Can you do that and then I will merge.