refactor: centralize circular query dependency detection (backport #1032)

[mergify]

Replaces 4 independent, ad-hoc circular reference guards with a unified approach:

• New query_utils.py: shared graph utilities — extract_query_deps_from_operations, get_direct_dependencies, transitive_closure, find_cycle
• Validate on save (InsightsQueryv3.validate): cycles are now caught before being persisted, with a full cycle path in the error message (e.g. "A" → "B" → "A")
• IbisQueryBuilder.build(): owns the runtime recursion guard (via frappe.local) as a defensive fallback
• get_source_tables(): rewritten using transitive_closure — drops the recursive visited parameter pattern
• set_linked_queries(): simplified to a one-liner using extract_query_deps_from_operations
• getLinkedQueries() (frontend): fixed a latent infinite-loop bug — adds a _visited Set to guard against cycles in already-loaded data
• getEffectiveOperationsForDrillDown() (frontend): _visitedQueryNames: string[] → _visitedQueries: Set<string> for O(1) lookups and consistent style

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  This is an automatic backport of pull request refactor: centralize circular query dependency detection #1032 done by Mergify.