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fix(cypher): deliver EXPLAIN/PROFILE plans to Bolt and HTTP clients (#744)

Plans were built on EXPLAIN/PROFILE but never serialized to clients:
Bolt PULL SUCCESS metadata and HTTP transaction results omitted them.

- Bolt: the final SUCCESS metadata now carries "plan" (EXPLAIN) and
  "profile" with runtime counters (PROFILE); the Go driver exposes both
  via summary.Plan() / summary.Profile(). Ordinary queries send neither.
- HTTP: transaction results carry "plan"/"profile" in the Neo4j JSON
  shape: operatorType, identifiers, args with EstimatedRows, children;
  profile adds rows/dbHits.
- Convergence: one Neo4jPlanMap renderer in pkg/cypher feeds both
  protocols from the same ExecutionPlan tree.

Also fixes a plan-leak bug the tests exposed: PROFILE's inner execution
served and populated the result cache, then attachPlanMetadata mutated the
shared cached result object, handing plan metadata to ordinary cached reads
of the same query. PROFILE now bypasses the result cache on both read and
write (context marker checked only after the cheap cache gates).

Performance (M2 Max, -cpu=1 -count=3 -benchtime=300ms,
BenchmarkStatementRouting, same checkout with changes stashed):

  autocommit/simple_match_limit  main  17733-18056 ns/op, 161 allocs/op
                                 fixed 17917-18381 ns/op, 161 allocs/op
  explicit_tx/simple_match_limit main  11546-13441 ns/op,  88 allocs/op
                                 fixed 11462-11714 ns/op,  88 allocs/op

Allocation-identical; latency within run-to-run noise. The northwind
Neo4j-vs-NornicDB comparison is untouched by this change (EXPLAIN/PROFILE
delivery only); per request it is not a gate for this PR.

Tests: cypher unit (Neo4jPlanMap shape, counters on/off), Bolt driver
end-to-end (summary.Plan/Profile populated, ordinary queries nil), HTTP
end-to-end (plan/profile keys), each asserted deeply. Full pkg/cypher,
pkg/bolt, pkg/server suites, -race on the new tests, and the TCK ratchet
(7794/7794, 100%) pass.