Replace spansql with memefish v0.4.0

[nktks]

This PR is created by Cline.

This PR replaces the spansql dependency with memefish v0.4.0. The main changes are:

1. Updated the go.mod file to add the memefish v0.4.0 dependency and remove the cloud.google.com/go/spanner dependency.
2. Modified the cli.go file to use memefish parser instead of spansql parser.
3. Updated the graph.go file to use memefish AST types instead of spansql types.

The parser now correctly handles SQL statements separated by semicolons, which fixes the issue with empty ER diagrams.

[Copilot]

Pull Request Overview

This PR replaces the spansql dependency with memefish v0.4.0, updating the parsing and graph generation logic accordingly.

• Dependency update and import modifications in cli.go and graph.go
• Updated SQL parsing in cli.go to handle semicolon-separated statements
• Adjusted graph generation logic in graph.go to work with memefish AST types

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
cli.go	Replaces spansql with memefish, updates parsing logic and adds detailed logging, and improves dot command error handling
graph.go	Updates functions to use memefish AST types and refines table node and foreign key edge handling

Comments suppressed due to low confidence (2)

cli.go:132

• Parsing errors are currently only logged and then skipped, which may lead to silently ignoring failed SQL statements. Consider returning an error or accumulating errors to make the failure more explicit.

if err != nil { log.Printf("Error parsing statement: %v", err) continue }

graph.go:120

• [nitpick] The comment above refers to 'Handle interleave' even though the code uses the 'Cluster' field; updating the comment to reflect the correct field may improve clarity.

if t.Cluster != nil {