fix: Convert big integers to float64

Large numbers can be returned by the Flexpool API reaching the `int64`
limit. Blocks reward were seen as 0 ETH. Using `float64` instead. Also
converting signed int64 to unsigned int64 for non-timestamp numbers.

BREAKING CHANGE: please follow the upgrades instructions from 1.2 to
1.3 to convert such types in the database.

Signed-off-by: Julien Riou <julien@riou.xyz>

migrations/1.2_to_1.3.sql

@@ -0,0 +1,28 @@
+-- Migrate from 1.2 to 1.3
+-- SQLite doesn't support ALTER TABLE... ALTER TYPE
+-- This migration file creates the new structures with "real" types
+-- instead of "integer", move data to this new table then drop the old one.
+
+-- miners
+
+ALTER TABLE `miners` RENAME TO `miners_old`;
+
+CREATE TABLE `miners` (
+    `id` integer,
+    `created_at` datetime,
+    `updated_at` datetime,
+    `deleted_at` datetime,
+    `coin` text,
+    `address` text NOT NULL UNIQUE,
+    `balance` real,
+    `last_payment_timestamp` integer,
+    PRIMARY KEY (`id`)
+);
+
+INSERT INTO `miners` SELECT * FROM `miners_old`;
+
+DROP TABLE `miners_old`;
+
+CREATE INDEX `idx_miners_deleted_at` ON `miners`(`deleted_at`);
+
+SELECT "Database migrated to 1.3"