[Refactor] migrate pkg/errors to Crossplane Errors

[siddimore]

Description of your changes

Migrate from deprecated github.com/pkg/errors to github.com/crossplane/crossplane-runtime/v2/pkg/errors.

Why:

github.com/pkg/errors is no longer actively developed and is in maintenance mode since 2021

• The codebase was inconsistently using both pkg/errors and crossplane-runtime/v2/pkg/errors.
• crossplane-runtime/v2/pkg/errors provides native Go 1.13+ error wrapping compatibility (errors.Is/errors.As) plus crossplane-specific utilities like WithSilentRequeueOnConflict
• Reduces direct dependency footprint (pkg/errors is now only an indirect dependency)

Changes:

• Replace all direct imports of github.com/pkg/errors with github.com/crossplane/crossplane-runtime/v2/pkg/errors
• Use xperrors alias in reconciler.go files to disambiguate from kerrors (k8s api errors)
• Run go mod tidy to clean up dependencies

FilesChanged:

• client: upbound, aws, gke, azure, client.go, ssa/cache/extractor
• cluster: object, observedobjectcollection
• namespaced: object, observedobjectcollection

I have:

• Read and followed Crossplane's contribution process.
• Run make reviewable test to ensure this PR is ready for review.

How has this code been tested

• All 219+ unit tests pass (go test)
• Build succeeds (go build)
• go vet passes with no issues
• Import changes are mechanical (find/replace) with no logic changes