feat: add duration data model

[akrigline]

Examples

Magic Missile
Duration: Instantaneous

{
  type: 'instantaneous',
}

---

Comprehend Languages
Duration: 1 hour

{
  type: 'time',
  rounds: 600,
}

---

Mage Armor
Duration: 8 hours

{
  type: 'time',
  rounds: 4800, // 600 * 8
}

---

Shield (assuming unchanged from SRD 5.1)
Duration: 1 round
...Until the start of your next turn

{
  type: 'time',
  rounds: 1,
  special: 'start of your next turn'
}

[cswendrowski]

I think we can probably do better than special, such as effectEnds. Perhaps we can offer choices? Off the top of my head, I can think of the following options:

• Start of Round
• End of Round
• Start of Target's Turn
• End of Target's Turn
• Start of Caster's Turn
• End of Caster's Turn
• None (purely time based)

We may also want to have a Concentration choice, or perhaps Concentration is a bool on the duration

[cswendrowski]

We'll want to localize these, probably with a label on top of a machine-friendly unit that we already have

[cswendrowski]

Great work, left some thoughts but feel free to merge as-is