TF-42218 Replaces repeated generated-HCL string concatenation with per-address builders
The Issue & Context
The `terraform query -generate-config-out` command was slow and memory-heavy when generating large HCL config outputs due to repeated string concatenations accumulating generated HCL text.
Root Cause Analysis
The old implementation used repeated string concatenation for each address's generated HCL, causing quadratic time complexity and excessive memory allocations as the output size grew, especially visible in `internal/cloud/backend_query.go`.
Solution Strategy & Architectural Pattern
This PR introduced per-address `*strings.Builder` instances to accumulate generated HCL blocks linearly, preserving grouping for interleaved lists and existing output behavior, drastically reducing allocations and improving runtime performance.
Key Takeaway for Contributors
Avoid repeated string concatenation in large-scale text generation; use dedicated builders or buffers per logical unit to achieve linear time complexity and reduce GC pressure.