Add Support for Querying Against Read Replicas

[smst-jeff]

This PR adds support for querying against read replicas, in a round-robin fashion.

This PR also cleans up some comments and closes a rows resource that was never closed.

[Copilot]

Pull request overview

This PR adds support for querying against read replicas in a round-robin fashion, allowing applications to distribute read operations across multiple database connections.

Changes:

• Added read replica infrastructure with circular linked list implementation for round-robin connection selection
• Implemented new query methods (QueryRR, QueryRowRR, GetRR, GetAllRR) that execute against read replicas
• Fixed a resource leak where rows was not being closed in the GetAll method

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
read_replicas.go	Implements core read replica functionality with thread-safe round-robin connection management
read_replicas_test.go	Comprehensive unit tests for read replica add and next operations
sequel.go	Adds read replica field to DB struct, new RR query methods, and fixes missing rows.Close()
sequel_test.go	Integration tests for read replica query operations with multiple database connections
main_test.go	Refactors test setup to create three database containers (one master, two read replicas)
testdata/init-db-rr.sh	Initialization script for read replica test databases with sample data

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[Copilot]

The loop condition c != first will never be true on the first iteration since c is initialized to first. This means the loop will never execute and connections will not be closed. The condition should check if c.next != first or restructure to use a do-while pattern.

Suggested change

	first := rr.current
	for c := first; c != first; c = c.next {
	c.db.Close()
	if rr.current == nil {
	return
	}
	first := rr.current
	for c := first; ; c = c.next {
	c.db.Close()
	if c.next == first {
	break
	}