refactor: Convert MoneyAmount to INTEGER cents storage and modularize currency types

- Refactor MoneyAmount to store as INTEGER cents instead of TEXT decimals
- Move CurrencyType to separate currency_type.rs module
- Rename money.rs to money_amount.rs for clarity
- Update database schema to use INTEGER for all monetary columns
- Remove complex CAST AS REAL workarounds from database queries
- Add comprehensive test coverage for cent-based arithmetic and storage
- Enable STRICT mode and foreign key constraints in SQLite
- Add rstest dependency for parameterized testing

Benefits:
- Faster INTEGER-based comparisons vs TEXT casting
- Exact financial precision without floating-point errors
- Simpler, cleaner SQL queries
- Better performance for auction bid operations

migrations/20240827001_initial_schema.sql

@@ -1,5 +1,8 @@
 -- Initial database schema for Pawctioneer Bot
--- Supports all listing types: standard, multi_slot, fixed_price, blind
+-- Supports all listing types: basic_auction, multi_slot_auction, fixed_price_listing, blind_auction
+
+-- Enable foreign key constraints
+PRAGMA foreign_keys = ON;
 
 -- Core user tracking
 CREATE TABLE users (
@@ -10,20 +13,20 @@ CREATE TABLE users (
     is_banned BOOLEAN DEFAULT FALSE,
     created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
     updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
-);
+) STRICT;
 
 -- Main listing table (handles all listing types)
 CREATE TABLE listings (
     id INTEGER PRIMARY KEY,
     seller_id INTEGER NOT NULL,
-    listing_type TEXT NOT NULL, -- 'standard', 'multi_slot', 'fixed_price', 'blind'
+    listing_type TEXT NOT NULL, -- 'basic_auction', 'multi_slot_auction', 'fixed_price_listing', 'blind_auction'
     title TEXT NOT NULL,
     description TEXT,
 
-    -- Pricing
-    starting_bid DECIMAL(10,2),
-    buy_now_price DECIMAL(10,2),
-    min_increment DECIMAL(10,2) DEFAULT 1.00,
+    -- Pricing (stored as INTEGER cents for USD)
+    starting_bid INTEGER,
+    buy_now_price INTEGER,
+    min_increment INTEGER DEFAULT 100, -- 1.00 USD = 100 cents
 
     -- Multi-slot/fixed price
     slots_available INTEGER DEFAULT 1,
@@ -36,14 +39,14 @@ CREATE TABLE listings (
     created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
     updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
     FOREIGN KEY (seller_id) REFERENCES users(id)
-);
+) STRICT;
 
 -- Proxy bid strategies (NOT actual bids, but bidding strategies)
 CREATE TABLE proxy_bids (
     id INTEGER PRIMARY KEY,
     listing_id INTEGER NOT NULL,
     buyer_id INTEGER NOT NULL,
-    max_amount DECIMAL(10,2) NOT NULL,
+    max_amount INTEGER NOT NULL, -- stored as cents
     is_active BOOLEAN DEFAULT TRUE,
 
     created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
@@ -52,14 +55,14 @@ CREATE TABLE proxy_bids (
     FOREIGN KEY (listing_id) REFERENCES listings(id),
     FOREIGN KEY (buyer_id) REFERENCES users(id),
     UNIQUE(listing_id, buyer_id) -- One active proxy per user per listing
-);
+) STRICT;
 
 -- Actual bids that happened (events)
 CREATE TABLE bids (
     id INTEGER PRIMARY KEY,
     listing_id INTEGER NOT NULL,
     buyer_id INTEGER NOT NULL,
-    bid_amount DECIMAL(10,2) NOT NULL,
+    bid_amount INTEGER NOT NULL, -- stored as cents
 
     -- For blind listings
     description TEXT,
@@ -76,7 +79,7 @@ CREATE TABLE bids (
     FOREIGN KEY (listing_id) REFERENCES listings(id),
     FOREIGN KEY (buyer_id) REFERENCES users(id),
     FOREIGN KEY (proxy_bid_id) REFERENCES proxy_bids(id)
-);
+) STRICT;
 
 -- Media attachments
 CREATE TABLE listing_medias (
@@ -88,7 +91,7 @@ CREATE TABLE listing_medias (
     created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
     updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
     FOREIGN KEY (listing_id) REFERENCES listings(id)
-);
+) STRICT;
 
 -- User preferences
 CREATE TABLE user_settings (
@@ -99,7 +102,7 @@ CREATE TABLE user_settings (
     created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
     updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
     FOREIGN KEY (user_id) REFERENCES users(id)
-);
+) STRICT;
 
 -- Create indexes for better performance
 CREATE INDEX idx_listings_seller_id ON listings(seller_id);