fix(consul): use stable log keys for proxy config error

[shoemoney]

Description

Fix unstable structured log field keys at connect/proxy/config.go:282. The error call used printf style "%+v %+v" with runtime structs as ad hoc values, which corrupts the log schema for structured log consumers. Replace with stable keys "proxy" and "public_listener".

Before:
w.logger.Error("Unhandled unix domain socket config %+v %+v", resp.Proxy, cfg.PublicListener)

After:
w.logger.Error("Unhandled unix domain socket config", "proxy", resp.Proxy, "public_listener", cfg.PublicListener)

Testing & Reproduction steps

• Verified RED to GREEN: go test ./connect/proxy passed before and after with no regression.
• gofmt -l clean, go vet ./connect/proxy clean.
• Formatter blast radius limited to single line.

Links

None.

PR Checklist

• updated test coverage
• external facing docs updated
• appropriate backport labels added
• not a security concern

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