fix: resolve golangci-lint exclusions — QF1012 WriteString+Sprintf style issues

[tekenstam]

Background

When golangci-lint v2 was introduced as part of the deps update in #521, two categories of pre-existing staticcheck issues were suppressed in `.golangci.yml`:

1. SA1019 — aws-sdk-go v1 deprecation warnings — tracked in feat: migrate from aws-sdk-go v1 to aws-sdk-go-v2 #523 (migrate to v2 SDK)
2. QF1012 — `WriteString(fmt.Sprintf(...))` style issues — tracked here

Once #523 is resolved, the SA1019 exclusion can also be removed.

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QF1012 Issues to Fix

`controllers/provisioners/eks/helpers.go`:

Line	Current	Fix
621	`sb.WriteString(fmt.Sprintf("-Base64ClusterCA %v ", aws.StringValue(state.Cluster.CertificateAuthority.Data)))`	`fmt.Fprintf(&sb, "-Base64ClusterCA %v ", aws.StringValue(...))`
622	`sb.WriteString(fmt.Sprintf("-APIServerEndpoint %v ", aws.StringValue(state.Cluster.Endpoint)))`	`fmt.Fprintf(&sb, "-APIServerEndpoint %v ", aws.StringValue(...))`
625	`sb.WriteString(fmt.Sprintf("-ContainerRuntime %v ", bootstrapOptions.ContainerRuntime))`	`fmt.Fprintf(&sb, "-ContainerRuntime %v ", bootstrapOptions.ContainerRuntime)`
627	`sb.WriteString(fmt.Sprintf("-KubeletExtraArgs '%v'", ctx.GetKubeletExtraArgs()))`	`fmt.Fprintf(&sb, "-KubeletExtraArgs '%v'", ctx.GetKubeletExtraArgs())`

Note: `fmt.Fprintf` writes directly to the `strings.Builder` without allocating an intermediate string.

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Definition of Done

• All 4 QF1012 occurrences in `helpers.go` are rewritten using `fmt.Fprintf`
• The `QF1012` rule is removed from `.golangci.yml`
• The `SA1019` rule is removed from `.golangci.yml` as part of the v2 SDK migration (feat: migrate from aws-sdk-go v1 to aws-sdk-go-v2 #523)
• `golangci-lint run ./...` passes with no exclusion rules