feat: implement topological dependency planner

[bella-247]

This pull request introduces new logic for handling table dependency resolution in the presence of foreign key cycles and blocked tables in the planner package. The changes implement robust algorithms (including Tarjan's strongly connected components and Kahn's topological sort) to analyze and resolve cycles, identify blocked tables, and determine a valid generation order for tables based on their dependencies.

The most important changes are:

Cycle Detection and Resolution:

• Added cycles.go with functions to detect strongly connected components (cycles) using Tarjan's algorithm, determine true cycles, and resolve them by identifying nullable foreign key breakpoints and producing table generation plans that defer certain foreign keys when necessary.

Topological Sorting and Blocked Table Handling:

• Added topsort.go implementing Kahn’s algorithm for topological sorting of tables by their foreign key dependencies, and for identifying tables that are blocked or involved in cycles.
• Added blocked.go to process tables that are blocked (not in a true cycle but dependent on unresolved cycles), allowing them to be generated once their dependencies are resolved, and reporting errors if any remain unresolvable.## What does this PR do?

Why is it needed?

Closes #

How was it tested?

Does it change any existing behavior?

Checklist

• Tests added or updated
• make test passes (go test ./... -race)
• make lint passes (golangci-lint run ./...)
• No cross-stage imports (parser doesn't import generator, etc.)
• No time.Now() or unseeded randomness in the generation pipeline
• Error messages follow the format in SRS §12.2
• Exported functions have doc comments
• Golden files updated if output format changed (make test-golden UPDATE=true)

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