fix(gcp): fold FOLD-1047 code quality / correctness findings into fix/gcp-recs-count-pricing

[cristim]

Problem

This issue tracks the FOLD-1047 findings from the remaining-findings plan (docs/code-review/16-remaining-findings-plan.md). These are medium/low/nit-severity findings whose files are already modified by PR #1047.

Findings

ID	File:Line	Sev	Fix
10-M2	computeengine/client.go:350-353,508-511,574-577 + cloudsql/memorystore/cloudstorage	Med	Add termPlan(term) helper + named memMBPerVCPU const; dedup the 4096/term mapping
10-M3	computeengine/client.go:377-384	Med	Typed retry classification (errors.As *googleapi.Error{Code:429} + status.FromError codes.ResourceExhausted) instead of substring match
10-M5	gcp/{computeengine:804,cloudsql,memorystore,cloudstorage}	Med	Derive PaymentOption from params, default to "monthly" (GCP CUDs have no upfront option) -- supersedes #829/#718 which also stamp monthly
10-M6	gcp/{computeengine:71,cloudsql:46,memorystore:57,cloudstorage:56},provider.go:95	Med	Remove struct-stored ctx field (containedctx lint); pass ctx per call
10-M7	gcp/provider.go:336-344	Med	GetAccounts: return empty on zero ACTIVE projects instead of synthesizing an account
10-L1	computeengine/client.go:293-296	Low	Fix no-op commitmentType branch (both arms assign CommitmentCUD)
10-L2	cloudstorage/client.go:228-242	Low	GetExistingCommitments should return empty (GCS has no commitment API), not every regional bucket
10-L3	cloudsql/client.go:210-231	Low	Don't treat legacy PricingPlan=="PACKAGE" as a commitment
10-L4	memorystore/client.go:122-124	Low	Wrap in realRecommenderIterator like the other 3 clients for diffability
10-N1	computeengine/client.go:888-894	Nit	Single common.Ptr[T] instead of per-package stringPtr/int64Ptr (deferred: common.Ptr[T] does not yet exist)
10-N3	recommendations.go:228	Nit	Rename local var shadowing the imported provider package

Also fixes CI (cyclomatic complexity > 10 in convertGCPRecommendation and extractVCPUCountFromRecommendation).

Fix

Additional commits on PR #1047 (fix/gcp-recs-count-pricing).

Notes

• 10-M1 (dead GroupCommitments/CommitmentRequest/ResourceCommitment): deferred pending owner confirmation (no-delete rule)
• 10-N1 deferred until common.Ptr[T] is introduced (likely by refactor(arch): provider-module fragmentation forces copy-paste (fan-out, env reader, savings formula); + pkg/errors orphan, logging split #1035 refactor)
• 10-N2 (cache SDK clients): skip, currently fine for Lambda as noted
• 10-M5 supersedes the monthly-stamp in PR fix(gcp): stamp PaymentOption=monthly on all GCP recs (closes #718) #829 (which stamps monthly in the purchase body but not in the default converter) -- see PR fix(gcp): wire Count/pricing into GCP converters; refuse fabricated prices #1047 body for detail