Cleanup: IDatabase* alignment

This will make maintenace and compares easy for adding sync/async operations. Next up: docs completion and syncing over.

StackExchange.Redis/StackExchange/Redis/RedisValueWithExpiry.cs

+using System;
+
+namespace StackExchange.Redis
+{
+    /// <summary>
+    /// Describes a value/expiry pair
+    /// </summary>
+    public struct RedisValueWithExpiry
+    {
+        internal RedisValueWithExpiry(RedisValue value, TimeSpan? expiry)
+        {
+            Value = value;
+            Expiry = expiry;
+        }
+
+        /// <summary>
+        /// The expiry of this record
+        /// </summary>
+        public TimeSpan? Expiry { get; }
+
+        /// <summary>
+        /// The value of this record
+        /// </summary>
+        public RedisValue Value { get; }
+    }
+}
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