GeezerVison

Fixes sqlc-dev#4448

Enum values containing backslashes, double quotes, or other special
characters were interpolated raw into the Go template:

    {{.Name}} {{.Type}} = "{{.Value}}"

This caused silent data corruption: a PostgreSQL enum value like
'user\nadmin' (literal backslash + n, 11 bytes) became the Go constant
"user\nadmin" (newline character, 10 bytes). Comparisons against the
database value silently fail at runtime.

Values containing double quotes broke go/format.Source() entirely.
Values like 'injected" + "code" + "' generated valid-but-wrong Go
string concatenation expressions.

Fix: replace "{{.Value}}" with {{printf "%q" .Value}}.

Go's %q verb produces a properly double-quoted, fully-escaped string
literal — backslashes are doubled, double quotes are escaped, control
characters use named sequences. The outer quotes are included by %q,
so no surrounding quotes are needed in the template.

Before: UserRoleUsernadmin UserRole = "user\nadmin"  // newline!
After:  UserRoleUsernadmin UserRole = "user\\nadmin" // correct

Regression tests added in internal/codegen/golang/enum_test.go covering:
- plain values (unchanged)
- literal backslash sequences (\n, \t, \\)
- embedded control characters
- double quotes in values
- string concatenation injection pattern