What type of PR is this?

/kind cleanup
/kind e2e

What this PR does / why we need it:

Refactors the e2e test framework from flat utility functions and a monolithic
TestContext struct into domain-specific manager structs with bound methods.

New packages:

• e2e/k8s/ — Clients, PodManager, NodeManager, ResourceManager, polling, conversions
• e2e/grove/ — WorkloadManager, TopologyVerifier, PodGroupVerifier, OperatorConfig
• e2e/diagnostics/ — DiagCollector
• e2e/tests/suite.go — TestSuite composing all managers with functional options

Key fixes:

• REST mapper is now created once in SharedClusterManager instead of being
  recreated per-test via CreateKubernetesClients
• Pre-existing build errors in rolling update tests resolved (bare function
  calls converted to TestSuite method calls)

Design for future parallel suites:

• TestSuite.Namespace is per-suite (can be unique for parallel runs)
• k8s.Clients is goroutine-safe (shared across suites)
• Managers are scoped to their suite instance, no global state

Which issue(s) this PR fixes:

Fixes #513
Fixes #513

Special notes for your reviewer:

• TestContext and its methods in setup.go/debug_utils.go are marked
  deprecated but kept — they are still used by the diagnostics path and will
  be removed in a follow-up once debug_utils.go consumers are fully migrated.
• The auto-mnnvl/ tests use their own lowercase testContext struct and were
  intentionally not migrated in this PR to keep scope manageable.
• The utils/ package files remain as deprecated wrappers. Only logger.go
  and measurement/ are long-term residents; the rest will be deleted in a
  follow-up PR.
• All e2e test files (startup ordering, scale, gang scheduling, topology,
  cert management, rolling updates) have been migrated to use TestSuite.

Does this PR introduce a API change?

NONE

Additional documentation e.g., enhancement proposals, usage docs, etc.:

 NONE