Remove double formatting in AST import replacer

[Copilot]

Addresses feedback from PR #4592 regarding inefficient double formatting of Go files during project generation.

Changes

• Replace format.Node with printer.Fprint in AST replacer to skip intermediate formatting
• Defer all formatting to final utils.GoFmt call which uses golang.org/x/tools/imports

Previously, files modified by the AST replacer were formatted twice—once during import path replacement and again by the final utils.GoFmt call. Now the AST replacer writes unformatted AST, and a single utils.GoFmt pass handles both formatting and import organization.

// Before: formatted output
if err := format.Node(&buf, r.fset, file); err != nil {
    return err
}

// After: unformatted output, formatting deferred
if err := printer.Fprint(&buf, r.fset, file); err != nil {
    return err
}

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