Expand attribute coverage for SDK spec options

[jmarbutt]

Problem

Attribute-based function registration only supports a subset of SDK spec options:

• ✅ Retry
• ✅ Concurrency
• ✅ Rate limit

Missing attributes for:

• ❌ Throttle
• ❌ Debounce
• ❌ Batch
• ❌ Cancellation
• ❌ Idempotency
• ❌ Priority

Location: Inngest/Internal/InngestFunctionRegistry.cs:200-231

Users who prefer the attribute-first pattern can't express large parts of the SDK spec today.

Suggested Solution

Add attributes for each missing option:

[Throttle(Limit = 10, Period = "1m", Key = "event.data.userId")]
[Debounce(Period = "5s", Key = "event.data.userId")]
[Batch(MaxSize = 100, Timeout = "10s")]
[Cancellation(Event = "order/cancelled", Match = "async.data.orderId == event.data.orderId")]
[Idempotency(Key = "event.data.orderId")]
[Priority(Run = "event.data.priority")]
public class MyFunction : IInngestFunction { }

Priority

Low - users can still use the fluent API for these options. This is a convenience/consistency improvement.