fix(apisix-standalone): potential duplication of global rules

[bzp2010]

Description

Fixes #489

Global rules are now parsed correctly during the dump, preventing potential plugin ID duplicates and redundant synchronization attempts.

The error mechanism has been described in some detail in #489.

Checklist

• I have explained the need for this PR and the problem it solves
• I have explained the changes or the new features added to this PR
• I have added tests corresponding to this change
• I have updated the documentation to reflect this change
• I have verified that this change is backward compatible

[coderabbitai]

📝 Walkthrough

Walkthrough

Fixes a bug in the APISIX standalone backend's toADC transformer where global_rules plugins were incorrectly accessed by array index (plugins![0]) instead of being iterated as a record. The fix flattens each rule's plugins map via Object.entries. A new E2E test suite validates the full global rule lifecycle including idempotency.

Changes

Global rules transformer fix and E2E validation

Layer / File(s)	Summary
toADC global_rules and plugin_metadata transformer fix libs/backend-apisix-standalone/src/transformer.ts	global_rules construction changes from gr.plugins![0] (array index, always undefined) to flatMap-ing Object.entries(gr.plugins ?? {}) and applying recursiveOmitUndefined per plugin value. plugin_metadata moves recursiveOmitUndefined to apply directly on the rest object instead of a separate .map pass over all entries.
Global Rule E2E lifecycle test suite libs/backend-apisix-standalone/e2e/resources/global-rule.e2e-spec.ts	Adds a complete Jest E2E suite covering: create two global rules and dump-verify, idempotent second sync (zero events, global_rules_conf_version unchanged), update one rule with a single UPDATE event, delete all rules with only DELETE events, and final dump confirming an empty rules list.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

🚥 Pre-merge checks | ✅ 6

✅ Passed checks (6 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The PR fully addresses issue #489 by fixing the plugins read path transformation, adding comprehensive e2e tests, and preventing duplicate global rule creation on resync.
Out of Scope Changes check	✅ Passed	All changes are directly related to fixing the global_rules read path bug and validating it through e2e tests; no out-of-scope modifications detected.
E2e Test Quality Review	✅ Passed	E2E test comprehensively covers the fix: CRUD lifecycle (create 2 rules, update, delete), critical idempotency regression test verifying zero diff events and stable conf_version on resync, proper r...
Security Check	✅ Passed	No security vulnerabilities found across all 7 categories: (1) No sensitive data exposure in logs—test has no logging, transformer has no new logging; (2) No database secrets—no persistence code ch...
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely identifies the main bug fix: a duplication issue with global rules in the apisix-standalone backend.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch bzp/fix-apisix-standalone-global-rules-dups

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