Controls how rounding is performed:

• halfExpand: Round to the nearest of the values allowed by roundingIncrement and smallestUnit. When there is a tie, round up. This mode is the default.
• ceil: Always round up, towards the end of time.
• trunc: Always round down, towards the beginning of time.
• floor: Also round down, towards the beginning of time. This mode acts the same as trunc, but it's included for consistency with Temporal.Duration.round() where negative values are allowed and trunc rounds towards zero, unlike floor which rounds towards negative infinity which is usually unexpected. For this reason, trunc is recommended for most use cases.