sdks/typescript: replace datetime / untyped duration types with Temporal

[Copilot]

Replace JavaScript Date with the Temporal API for datetime types, using temporal-polyfill as referenced in the issue.

Changes

• New temporal-types.ts module exporting:

  • Temporal.Instant for exact points in time
  • Temporal.Duration for time spans
  • Conversion helpers: instantFromDate, instantToDate, durationFromSeconds, durationToSeconds
  • Type guards: isInstant, isDuration

• sqlite.ts: datetime columns now decode to Temporal.Instant instead of Date

• sqlite-types.ts: SQLiteBindValue now accepts Temporal.Instant

Breaking Change

// Before
const run = await ctx.getRun(runID);
const epochMs = run.available_at.getTime();

// After  
const run = await ctx.getRun(runID);
const epochMs = run.available_at.epochMilliseconds;

// Or convert back to Date if needed
import { instantToDate } from "@absurd-sqlite/sdk";
const date = instantToDate(run.available_at);

Tests

Added 16 tests for Temporal type conversions and guards.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>sdks/typescript: replace datetime / untyped duration types with Temporal</issue_title>
<issue_description>Refs:

• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Temporal#browser_compatibility
• Temporal support (TC39 stage 3 proposal) oven-sh/bun#15853
• https://github.com/fullcalendar/temporal-polyfill</issue_description>

<agent_instructions>Please start with identifying usages first, then go minimal design & implementation; provide tests for the changes.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes sdks/typescript: replace datetime / untyped duration types with Temporal #22

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