fix(en): add index for fetching precommits (#4517)

## What ❔

Add one more index for supporting precommits query 
## Why ❔

En restart takes a long time
## Is this a breaking change?
- [ ] Yes
- [ ] No

## Operational changes
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## Checklist

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- [ ] PR title corresponds to the body of PR (we generate changelog
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- [ ] Tests for the changes have been added / updated.
- [ ] Documentation comments have been added / updated.
- [ ] Code has been formatted via `zkstack dev fmt` and `zkstack dev
lint`.

Signed-off-by: Danil <[email protected]>

Author: Deniallugo

core/lib/dal/migrations/20250929121423_index_for_fetching_precommits.down.sql

@@ -0,0 +1 @@
+DROP INDEX IF EXISTS miniblocks_number_precommit_not_null;

core/lib/dal/migrations/20250929121423_index_for_fetching_precommits.up.sql

@@ -0,0 +1,2 @@
+CREATE INDEX IF NOT EXISTS miniblocks_number_precommit_not_null ON miniblocks ( number )
+WHERE eth_precommit_tx_id IS NOT NULL;