refactor: extract generic protocol call helper for adapter package

[yvonnedevlinrh]

Context

The internal/adapter/ package contains four provider adapters that each implement the same Call + error check + json.Unmarshal pattern for communicating with external analyzers via JSON-RPC 2.0. This 8-line pattern is duplicated across complexity.go, coverage.go, sideeffect.go, and contract.go.

Additionally, safeSSABuild (the recover() guard around prog.Build()) is duplicated between internal/analysis/mutation.go and internal/quality/pairing.go.

Related: codebase audit from #166 triage

Patterns to Extract

Pattern	Files	Description
Protocol call + unmarshal	4 adapter files in internal/adapter/	resp, err := client.Call(ctx, method, params); if err != nil { return ..., err }; var result T; if err := json.Unmarshal(resp, &result); ...
safeSSABuild	internal/analysis/mutation.go, internal/quality/pairing.go	recover() guard around prog.Build() with warning log — identical implementation in both files

Proposed Changes

1. Add callAndUnmarshal[T any](client *protocol.Client, ctx context.Context, method string, params any) (T, error) generic helper to internal/adapter/ (or internal/protocol/)
2. Move safeSSABuild to a shared internal/ssautil/ package (or similar) and update both call sites

Acceptance Criteria

• Protocol call pattern has a single generic implementation
• All 4 adapter files use the shared helper
• safeSSABuild has a single source of truth
• Both analysis.BuildSSA and quality.BuildTestSSA use the shared version
• All existing tests pass without modification
• go test -race -count=1 -short ./... passes
• golangci-lint run reports zero issues