⚡ Bolt: optimize single-model inserts via direct streaming

[cungminh2710]

This change optimizes the SQL compilation path for single-model inserts in the Rain ORM.

By introducing a specialized writeSingleModelSQL method that uses stack-allocated buffers for values and column metadata, we bypass the creation of intermediate []assignment slices. This significantly reduces heap pressure and improves performance for one of the most frequent database operations.

Benchmark results for single-model insert compilation:

• Before: 3518 ns/op, 1144 B/op, 19 allocs/op
• After: 2298 ns/op, 792 B/op, 13 allocs/op
• Impact: ~35% speedup, ~31% fewer allocations.

The optimization is safely scoped to Model() calls without explicit .Set() overrides and includes a safe fallback for unusually large models.

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PR created automatically by Jules for task 14140129265122056175 started by @cungminh2710

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[greptile-apps]

Greptile Summary

This PR adds a faster SQL compilation path for single-model inserts. The main changes are:

• Direct streaming for model-only single-row inserts.
• Stack-backed buffers for common column and value lists.
• A documented optimization note in .jules/bolt.md.

Confidence Score: 5/5

This looks safe to merge.

• No blocking issues found in the changed code.
• The fast path is limited to model-only inserts without explicit value overrides.
• The new path uses the same model plan and insert-value filtering as the existing path.

Important Files Changed

Filename	Overview
pkg/rain/query_insert.go	Adds a guarded fast path for model-only inserts that mirrors the existing field selection and SQL writing behavior.
.jules/bolt.md	Documents the single-model insert optimization.

_{Reviews (1): Last reviewed commit: "perf(rain): optimize single-model insert..." | Re-trigger Greptile}