Fix parameter name collision in :one query return values

[kyleconroy]

Summary

This PR fixes a bug where :one queries would overwrite input parameters when the return value name collides with a parameter name, causing data corruption on sql.ErrNoRows errors.

Problem

When a :one query has a single return column with the same name as an input parameter, the generated code would reuse the parameter variable as the scan destination. This causes the Scan() call to overwrite the input parameter, and if sql.ErrNoRows is returned, the corrupted value leaks back to the caller.

Example of the bug:

func (q *Queries) GetAuthorIDByID(ctx context.Context, id int64) (int64, error) {
    row := q.db.QueryRow(ctx, getAuthorIDByID, id)
    err := row.Scan(&id)  // Overwrites input parameter!
    return id, err
}

Solution

For :one queries, the code generator now detects when the return variable name would collide with any parameter name and automatically renames the return variable by appending _2 (and further suffixes if needed).

Key Changes

• Modified buildQueries() in internal/codegen/golang/result.go to detect parameter name collisions for :one queries
• When a collision is detected, the return variable is renamed (e.g., id → id_2)
• Updated all affected test fixtures to reflect the corrected generated code

Implementation Details

• The collision detection only applies to :one queries (where the scan destination shares scope with parameters)
• A map of parameter names is built and checked against the return variable name
• If a collision exists, the return variable name is suffixed with _2, _3, etc. until no collision remains
• This ensures the scan destination is a separate variable that won't corrupt the input parameters

Fixes #4354

https://claude.ai/code/session_01Ly2rRRcRPXhT2bm6odjeqx