fix: sync CacheRuntime Client component spec on every reconcile

[adityaupasani2]

Ⅰ. Describe what this PR does

CacheRuntime's Client (FUSE) DaemonSet was never reconciled after initial creation. Any later change to runtime.spec.client.* (image/version, resources, tieredStore, volumes, env vars) was silently and permanently ignored, with no error or log indication.

Two compounding gaps caused this:

1. ShouldSetupClient() gates all client reconciliation on Status.Client.Phase == RuntimePhaseNone, which only holds true once, on the very first successful setup. SetupClientInternal (and therefore Reconciler()) never runs again for the runtime's lifetime.
2. DaemonSetManager.SyncComponentSpec was a stub that unconditionally returned an error, and syncRuntimeSpec (which DOES sync ongoing spec drift for Master/Worker) explicitly skipped Client, with a comment claiming it "will be recreated when spec changes" — no code anywhere actually implemented that.

This PR:

• Implements a real DaemonSetManager.SyncComponentSpec that diffs and patches image/resources, mirroring AdvancedStatefulSetManager's existing update pattern. Replicas is intentionally left unused since DaemonSet replica count is determined by node count, not user input.
• Wires Client into CacheEngine.syncRuntimeSpec so it's synced on every reconcile pass, same as Master/Worker already are.
• Fixes 7 test fixtures in sync_test.go where the client DaemonSet had no containers — harmless before since nothing ever touched it, but a legitimate (and correct) error once SyncComponentSpec actually runs against it, since a real DaemonSet always has at least one container.

Ⅱ. Does this pull request fix one issue?

Fixes #6154

Ⅲ. List the added test cases

New file pkg/ddc/cache/component/daemonset_sync_component_spec_test.go, mirroring the existing AdvancedStatefulSetManager test suite:

• SyncComponentSpec: image update (full/partial/unchanged), resources update (changed/unchanged), replicas ignored without error, multiple fields together, no-op when nothing changed, error when DaemonSet not found, error when DaemonSet has no containers
• updateImage / updateResources unit tests mirroring the AdvancedStatefulSetManager equivalents

Ⅳ. Describe how to verify it

1. Create a CacheRuntime with a Client component and wait for it to become ready.
2. Edit runtime.spec.client.resources (or bump the runtime version).
3. Before this fix: the Client DaemonSet's pod template is unchanged, no error anywhere. After this fix: the DaemonSet is patched and Kubernetes rolls the change out to the FUSE pods automatically.

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
41.4% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

❌ Patch coverage is 86.74699% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 65.19%. Comparing base (05f0665) to head (5f16e28).

Files with missing lines	Patch %	Lines
pkg/ddc/cache/engine/sync.go	63.15%	5 Missing and 2 partials ⚠️
pkg/ddc/cache/component/daemonset_manager.go	93.75%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6155      +/-   ##
==========================================
+ Coverage   65.13%   65.19%   +0.05%     
==========================================
  Files         485      485              
  Lines       34039    34120      +81     
==========================================
+ Hits        22171    22243      +72     
- Misses      10127    10133       +6     
- Partials     1741     1744       +3     

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