ntx-builder: move to sqlite framework

[SantiagoPittella]

closes #2250

Summary

Migrates the ntx-builder database layer off Diesel and onto the shared miden-node-db SQLite framework.

Why:

• Removes the last Diesel dependency and its schema/codegen tooling from the ntx-builder.
• Unifies persistence on one connection-pool + transaction model across the node.

How:

• Replaces the Diesel query modules with plain query functions over ReadTx/WriteTx and hand-written SQL in db/sql/.
• Drops the pinned "loop connection"; writes now serialize through the framework's single writer connection, reads use the shared reader pool.
• On-disk layout is unchanged (same to_bytes()/read_from_bytes() codec, same 001_initial.sql schema), so existing databases stay compatible.

Changelog

changelog = "none"
reason    = "Internal change only."

[Mirko-von-Leipzig]

Thank you!

[SantiagoPittella]

@Mirko-von-Leipzig should I merge or wait for some other approve?

[kkovaacs]

Looks good to me, thanks!