Test suite improvements for v1.0.0-beta.1

[leogdion]

Summary

Parent tracking issue for the test-related work targeted at the v1.0.0-beta.1 release. Covers coverage gaps, warning cleanup, organizational refactors, and an audit of existing assertions.

Sub-issues

• Fix Code Coverage Warnings #244 — Fix Code Coverage Warnings
• Test coverage: network errors, timeouts, and concurrent pagination for new operations #258 — Test coverage: network errors, timeouts, and concurrent pagination for new operations (lookupZones, fetchRecordChanges, uploadAssets)
• MistDemo: Reorganize tests using hierarchical enum+extension pattern #261 — MistDemo: Reorganize tests using hierarchical enum+extension pattern
• Run a Test and Assert Audit #262 — Run a Test and Assert Audit

Goal

Land all four before cutting v1.0.0-beta.1 so the released test suite is well-organized, free of coverage warnings, and exercises the new operations under realistic failure modes.