chore: sqlite framework

[SantiagoPittella]

closes #2248
closes #2249
closes #1465

Summary

Introduces a light SQLite framework in crates/db (miden-node-db) and migrates the validator onto it, removing Diesel. It handles a connection pool, type-enforced read/write transactions, always-cached queries, a type codec, and cacheable IN-list helpers.

• The framework keeps a small pool of connections alive and hands them out. Because SQLite is blocking, the actual query work runs on a background thread.
• We dont handle raw connections. The struct provides either a read or a write transaction and get a small
  handle:
  • read(...) gives you a ReadTx. It begins a read-only transaction that is never committed, so
    nothing it does can persist.
  • write(...) gives you a WriteTx. It begins a write transaction.
• Added verbs like query_rows, query_opt, query_one, exists, count and execute (write only). Every one of them prepares its statement through SQLite's cache.
• Added a codec to convert between native data types and sql's.

The usage is like this:

// a read
db.read("chain_tip", |tx| {
    tx.query_opt(
        "SELECT block_header FROM block_headers ORDER BY block_num DESC LIMIT 1",
        &[],
        |row| row.get::<BlockHeader>(0),
    )
}).await?;

// a write (several statements in one atomic transaction)
db.write("apply", move |tx| {
    tx.execute("INSERT INTO ... VALUES (?1, ?2)", &[&a, &b])?;
    tx.execute("UPDATE ... SET ... WHERE id = ?1", &[&id])?;
    Ok::<(), DatabaseError>(())
}).await?;

Changelog

[[entry]]
scope       = "internal"
impact      = "added"
description = "Bespoke SQLite framework aimed at replacing Diesel"

[[entry]]
scope       = "internal"
impact      = "changed"
description = "Validator now uses our own SQLite framework instead of Diesel"

[kkovaacs]

Apart from the single nit I've added I think this looks good!

Thanks!

[kkovaacs]

Neat!

[Mirko-von-Leipzig]

Yeah super cool!

[Mirko-von-Leipzig]

Yeah super cool!

[Mirko-von-Leipzig]

I think we should consider moving the sql into dedicated .sql files.

This allows for:

• SQL syntax highlighting and LSP
• linting
• formatting
• not fighting the rust indentations

This is slightly less relevant here, since we have so few; but I'm thinking a structure like:

bin/validator/src/db/queries
  /insert_transaction
    mod.rs
    tests.rs
    insert_transaction.sql
  /transaction_exists
    mod.rs
    tests.rs
    transaction_exists.sql
  /...

Doesn't need to be part of this PR though.

[Mirko-von-Leipzig]

I would caution against this; there are some edge cases here that are non-obvious. See my impl from previous job.

Instead, I would suggest using tmpdir/tmpfile to create a concrete but temporary db.

[Mirko-von-Leipzig]

Nit: read_only seems like a better name to me.