Keep extension data source state durable

[IlyaasK]

Summary

• remove runtime last_used_at from the kernel_extension data-source schema and state model
• ignore SDK usage timestamps when flattening extension metadata
• update focused schema/state tests and generated Terraform docs

Why this is v0 work

Terraform manages durable desired configuration. Extension usage timestamps change at runtime and would make data-source state depend on browser activity, so they must not enter the provider’s durable state boundary.

Tests

• go test -short -timeout=2m ./...
• go test -race -short -timeout=2m ./internal/datasources/extension
• go vet ./...
• go mod verify
• go mod tidy -diff
• terraform fmt -check -recursive examples
• bash scripts/check-markdown-links.sh
• bash scripts/check-docs.sh
• git diff --check
• gofmt -l cmd internal

Acceptance status

No live API operation is required for this schema correction. The stacked extension data-source acceptance PR verifies stable live metadata and a no-drift plan.

Intentionally unsupported

• no runtime usage timestamps in Terraform state
• no Terraform extension resource
• no extension download or Chrome Store operations

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Note

Medium Risk
Breaking schema change for anyone depending on last_used_at in configs or modules; behavior is intentional but requires consumer updates.

Overview
Removes last_used_at from the kernel_extension data source so Terraform state only holds durable extension metadata (id, name, project_id, created_at, size_bytes). Usage timestamps from the API are no longer mapped in flattenExtension or exposed in the schema.

Generated docs and tests are updated accordingly, including asserting last_used_at is absent from the schema and removing nullable last_used_at read coverage.

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