Go SDK: generate one query method per operator, with Verify and TargetLimit on probabilistic terms #1189

Background

The Go SDK's generated code has one query method per field: users.Fields.Email.Query(ctx, cipher, v), which returns the field's query operand, with the term chosen by the field's EQL type. ADR-0009 appendix B sketches the Go SDK under the operator model.

Problem

A Go caller cannot ask for a particular operator, cannot pass operator-specific input such as Between's two bounds, and gets no help verifying the results of a probabilistic query.

Proposal

• stashgen generates one method per operator the field's EQL type answers, with the operator's input in the signature, such as Fields.Name.Matches(ctx, cipher, "ali") and Fields.Age.Between(ctx, cipher, lo, hi). A field whose type does not answer an operator has no such method.
• stashgen takes the operators and their fidelity from the engine catalog, and holds no copy of those rules.
• The query types of probabilistic operators carry Verify and TargetLimit, and exact ones carry neither. Each keeps driver.Valuer.
• Verify over a page of rows is one call into the guest.
• Each Go width rule holds in the generated signatures.
• The README and doc.go show the query with database/sql and the decrypt-and-verify step.
• Hermetic tests against the guest, and a PostgreSQL test that runs a Matches query and verifies its rows.

Related

• Depends on Amend ADR-0007 for operator queries, and add the guest's query, verify and target_limit exports #1188.
• stashgen refuses TextMatch, TextSearch, TextOrd and TextOrdOpe — the engine derives their terms, but no EQL type is built from them #1131: TextMatch in the Go SDK.
• Go SDK: no test stores a generated type through database/sql, pgx, sqlc or GORM — add a PostgreSQL job #1114: storing a generated type through database/sql, pgx, sqlc and GORM.
• docs(adr): ADR-0009, operators select the index and a query term is not the stored term #1177: ADR-0009, appendix B.