tlv: add utility funcs/methods to make tlv.OptionalRecord easier to use

We add a WhenSome that'll pass in the actual underlying value, and not
just the record.

We also add `SomeRecord` to make it easier to create TLV records w/
`Some` set.

tlv/record_type.go

@@ -102,6 +102,21 @@ func (t *OptionalRecordT[T, V]) TlvType() Type {
 	return zeroRecord.TlvType()
 }
 
+// WhenSomeV executes the given function if the optional record is present.
+// This operates on the inner most type, V, which is the value of the record.
+func (t *OptionalRecordT[T, V]) WhenSomeV(f func(V)) {
+	t.Option.WhenSome(func(r RecordT[T, V]) {
+		f(r.Val)
+	})
+}
+
+// SomeRecordT creates a new OptionalRecordT type from a given RecordT type.
+func SomeRecordT[T TlvType, V any](record RecordT[T, V]) OptionalRecordT[T, V] {
+	return OptionalRecordT[T, V]{
+		Option: fn.Some(record),
+	}
+}
+
 // ZeroRecordT returns a zero value of the RecordT type.
 func ZeroRecordT[T TlvType, V any]() RecordT[T, V] {
 	var v V