Bind go-ruby-redis, go-ruby-pg and go-ruby-sequel into rbgo as native modules

[tannevaled]

Binds three database libraries into rbgo (require "redis" / require "pg" / require "sequel") as native modules, following the proven per-module pattern (<mod>.go + <mod>_bind.go, registered in builtins.go, providedFeatures in require.go, value wrappers wired into object_model.go's classOf).

Ruby API per module

redis — Redis.new(connection: io, db:, username:, password:, protocol:) plus the command surface: get/set/setnx/getset/append/incr/decr family, hset/hget/hgetall/hdel/hmget (hashes), lpush/rpush/lpop/lrange (lists), sadd/smembers/sismember (sets), zadd/zscore/zrange/zrank (sorted sets), call (arbitrary command), pipelined { |p| ... } and multi { |m| ... }. Value model: string→String, int64→Integer, float64→Float, bool→true|false, nil→nil, Array→Array, Map→Hash, Set→Set, big number → Integer, CommandError → a raised Redis::CommandError. Error tree Redis::BaseError < StandardError with CommandError / ConnectionError.

pg — PG.connect(connection: io, user:, dbname:/database:, password:, ...) drives the StartupMessage + AuthenticationOk/MD5/SCRAM handshake, then conn.exec/query/exec_params/prepare/exec_prepared → PG::Result (ntuples/nfields/fields/fname/fnumber/getvalue/getisnull/values/[]→Hash/each/cmd_tuples/cmd_status) with the OID type decoders, plus escape_string/escape_literal/escape_identifier/quote_ident. Error tree PG::Error < StandardError with ConnectionBad / ServerError.

sequel — Sequel.sqlite(path) / Sequel.connect(adapter:/URL) / Sequel.mock(host:) → Sequel::Database; DB[:table] → Sequel::Dataset with the chainable builders (where/exclude/select/order/reverse/group/having/distinct/limit/offset/join/inner_join/left_join/right_join) and terminals (sql/select_sql/insert_sql/update_sql/delete_sql/all/first/each/count/insert/update/delete); schema DSL via create_table(:t) { ... } (primary_key, typed columns String/Integer/Bignum/Float/Numeric/Bool/Date/DateTime/Time, column, foreign_key, index). Sequel::Model deferred.

Seams wired to what

• redis / pg socket seam — rbgo has no native TCPSocket yet, so both take an injected IO-like connection (any object responding to #read/#write, e.g. a duck-typed socket). rubyConn bridges that object to the libraries' io.ReadWriter Conn; pg's PasswordAuthenticator drives MD5/SCRAM over it. Documented in the binding headers. When rbgo grows a native socket it is wired here the same way.
• sequel executor seam — wired to go-ruby-sqlite3 (already bound as a real, functional DB). sqliteExecutor runs generated SQL through ExecuteHash.

sequel → sqlite3 real execution: yes

DB[:t].all / first / count really run the generated SELECT against a live in-memory SQLite database and return live rows; create_table / insert / update / delete execute their DDL/DML for real, with insert returning the SQLite last_insert_rowid and update/delete the affected-row count.

Gates

• rbgo builds; full go test ./... green (the one failure, TestChronicParse, is a pre-existing TZ-dependent test that passes under TZ=UTC as CI runs — unrelated to this PR).
• 100% coverage on all new binding code (redis.go/redis_bind.go/pg.go/pg_bind.go/sequel.go/sequel_bind.go/sequel_schema.go), including socket-seam error paths (via injected fake sockets and canned RESP / PostgreSQL v3 backend byte streams) and executor error paths; genuinely-dead guards were deleted.
• gofmt + go vet clean.

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