Implemented API support for set_limit (sqlite3_limit) in sqlite

[LucaCappelletti94]

This PR exposes SQLite's sqlite3_limit API through new methods on SqliteConnection. It is another PR in the series of: "let's make more of SQLite usable with Diesel in frontend WASM development", but it really applies to many other cases.

Motivation

SQLite's security documentation explicitly recommends using sqlite3_limit() for hardening:

Reduce the limits that SQLite imposes on inputs. This can help prevent denial of service attacks and other kinds of mischief that can occur as a result of unusually large inputs. You can do this either at compile-time using -DSQLITE_MAX_... options, or at run-time using the sqlite3_limit() interface.

The documentation also notes: "Most applications can reduce limits dramatically without impacting functionality."

SQLite's limits documentation provides specific context:

• CompoundSelect: Defaults to 500, but "in practice we almost never see the number of terms in a compound select exceed single digits"
• ExprDepth: Can prevent stack exhaustion from deeply nested expressions
• SqlLength: The security page suggests reducing from 1,000,000,000 to 100,000 for high-security deployments

While users could technically call the FFI directly, this PR provides a safe, ergonomic, and documented API that makes following SQLite's security recommendations straightforward.

Usage

Apply all recommended security limits in one call:

use diesel::sqlite::{SqliteConnection, SqliteLimit};
use diesel::Connection;

let mut conn = SqliteConnection::establish(":memory:")?;

// Apply SQLite's recommended high-security limits
conn.set_recommended_security_limits();

// Relax specific limits if needed for your application
conn.set_limit(SqliteLimit::VariableNumber, 999);

Or configure individual limits:

use diesel::sqlite::{SqliteConnection, SqliteLimit};
use diesel::Connection;

let mut conn = SqliteConnection::establish(":memory:")?;

// Limit SQL statement length to 100KB
conn.set_limit(SqliteLimit::SqlLength, 100_000);

// Prevent ReDoS via LIKE patterns
conn.set_limit(SqliteLimit::LikePatternLength, 100);

// Query current limits
let expr_depth = conn.get_limit(SqliteLimit::ExprDepth);

[LucaCappelletti94]

The compile test failures (mysql_on_conflict_tests.rs, pg_on_conflict_requires_valid_conflict_target.rs, update_requires_left_side_of_eq_to_be_a_column.rs) seem to be pre-existing on main and unrelated to this PR. They're caused by rustc error message formatting changes (e.g., Column vs diesel::Column in trait bounds).

I will do a quick separate PR to fix them later if that is correct and they are unrelated to this PR.