chore(golang): adopt #1094's third-review changes in the EQL build

#1094 renamed record.UInt64 to Uint64 and rewrote the generated
Encrypt/Decrypt comments to state the 500-value batch size; this
regenerates testusers.Contact and updates eql_test.go to match.

#1094 also moved the stashgen quick start to index= columns, because
that build refuses encrypt_into. This build produces TextEq, so the
quick start goes back to encrypt_into=TextEq with Fields.Email.Query,
and step 6 says what an eql.TextEq column binds as.

Claude-Session: https://claude.ai/code/session_01V3WFXwax4J3uecpFEJ6yHc

Author: coderdan

languages/golang/cmd/stashgen/README.md

@@ -21,8 +21,8 @@ Your program calls those functions, and it never builds or names a plan.
    type User struct {
    	_     struct{} `stash:"context=users"`
    	ID    int64    `stash:"id,passthrough"`
-   	Email string   `stash:"email,encrypt,index=equality;match"`
-   	Name  string   `stash:"name,encrypt"`
+   	Email string   `stash:"email,encrypt_into=TextEq"`
+   	Name  string   `stash:"name,encrypt_into=TextEq"`
    }
    ```
 
@@ -40,12 +40,11 @@ Your program calls those functions, and it never builds or names a plan.
    ```go
    encrypted, err := users.Encrypt(ctx, cipher, people)
    opened, err := users.Decrypt(ctx, cipher, encrypted)
-   term, err := users.Fields.Email.Equality(ctx, cipher, "bob@example.com")
+   query, err := users.Fields.Email.Query(ctx, cipher, "bob@example.com")
    ```
 
 6. Store the encrypted type.
-   Each sealed field is one or more byte columns: `Email.Ciphertext`, `Email.Equality`, `Email.Match`.
-   `encrypt.Ciphertext` and each term type implement `driver.Valuer` and `sql.Scanner`, so a database library binds and scans each one as bytes; map each one to its own column.
+   Each `encrypt_into` field is one EQL column: `eql.TextEq` implements `driver.Valuer` and `sql.Scanner`, so a database library binds and scans it as the JSON a `public.eql_v3_text_eq` column holds.
 
 7. Run the generator again after each change to the struct or to a tag.
    A change to the fields of the struct stops the build until you do.

languages/golang/encrypt/eql_test.go

@@ -322,7 +322,7 @@ func TestTextEqIsRefusedByTheBuildWithoutEQLTypes(t *testing.T) {
 		}
 	}
 	// A declared type other than TextEq's plaintext, and an extended plan.
-	wrongKind := &record.Plan{Context: []string{"users"}, Fields: []record.Field{{Name: "email", Kind: record.UInt64, Target: "TextEq"}}}
+	wrongKind := &record.Plan{Context: []string{"users"}, Fields: []record.Field{{Name: "email", Kind: record.Uint64, Target: "TextEq"}}}
 	if err := eqlChecker.Check(ctx, wrongKind); !errors.Is(err, encrypt.ErrEncoding) {
 		t.Errorf("a uint64 TextEq field: Check = %v, want ErrEncoding", err)
 	}