⚡ Bolt: Optimize single-model insert compilation performance

[cungminh2710]

This PR optimizes the SQL compilation path for single-model INSERT statements in Rain ORM.

By identifying that most inserts use a single model without additional .Set() overrides, we now bypass the expensive creation of intermediate assignment slices and map lookups. Instead, writeSingleModelSQL streams values directly from the model fields to the compilation context.

Additionally, we've optimized the assignment resolution logic with fast-paths for common primitive types (int64, int, string, bool), avoiding the overhead of reflect.Value.Interface() and associated boxing where possible.

Verification:

• New benchmark BenchmarkInsertToSQL/SingleModel shows a ~69% reduction in allocations and ~56% improvement in compilation speed.
• Full test suite passed via go test ./pkg/rain/....

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PR created automatically by Jules for task 15259031699631847227 started by @cungminh2710

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[greptile-apps]

Greptile Summary

This PR optimizes single-model insert SQL compilation in Rain ORM. The main changes are:

• Adds a direct single-model insert writer for .Model() without .Set() overrides.
• Adds primitive fast paths in model assignment resolution.
• Adds a benchmark for the optimized single-model insert path.

Confidence Score: 5/5

This looks safe to merge.

• No blocking issues found in the changed code.

Important Files Changed

Filename	Overview
pkg/rain/query_insert.go	Adds the direct single-model insert SQL path for model-only inserts.
pkg/rain/query_model_assignments.go	Adds guarded primitive fast paths for insert value resolution and auto-increment zero checks.
pkg/rain/compile_bench_test.go	Adds benchmark coverage for the single-model insert compilation path.

_{Reviews (2): Last reviewed commit: "refactor(rain): optimize single-model in..." | Re-trigger Greptile}

[cungminh2710]

@jules Fix the following 2 code review issues. Work through them one at a time, proposing concise fixes.

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Issue 1 of 2

pkg/rain/query_model_assignments.go:167-176
Primitive Providers Are Bypassed

When a model field uses a named primitive type such as a string or int wrapper with custom insert serialization, this branch returns the raw primitive before the existing interface-based value path can run. That changes Insert().Model(...).ToSQL() from using the custom database value to inserting the raw field contents.

Issue 2 of 2

pkg/rain/query_model_assignments.go:108-127
Auto ID Providers Are Skipped

For an auto-increment column backed by a named primitive field, a zero Go value is dropped here before the custom value path is consulted. A field that intentionally supplies its ID through custom serialization can now be omitted from the INSERT, leaving the database to generate a different value.

[google-labs-jules]

@jules Fix the following 2 code review issues. Work through them one at a time, proposing concise fixes.

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Issue 1 of 2

pkg/rain/query_model_assignments.go:167-176
Primitive Providers Are Bypassed

When a model field uses a named primitive type such as a string or int wrapper with custom insert serialization, this branch returns the raw primitive before the existing interface-based value path can run. That changes Insert().Model(...).ToSQL() from using the custom database value to inserting the raw field contents.

Issue 2 of 2

pkg/rain/query_model_assignments.go:108-127
Auto ID Providers Are Skipped

For an auto-increment column backed by a named primitive field, a zero Go value is dropped here before the custom value path is consulted. A field that intentionally supplies its ID through custom serialization can now be omitted from the INSERT, leaving the database to generate a different value.

I've addressed both issues by restricting the primitive fast-paths to built-in types (where PkgPath() == ""). This ensures that named primitive wrappers or custom providers implementing setValueProvider are correctly identified and processed through the standard interface-based path. Performance gains for standard types are preserved. Ready for review!