feat: Use new Nitro null types

[chrispader]

Makes use of the newly introduced NullType in Nitro. Replaces all occurences of the custom singelton SQLiteNullValue type with margelo::nitro::NullType

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Note

Medium Risk
Updates the native/JSI boundary and public TS types around nulls and query results, which can affect runtime behavior and downstream type expectations. Core DB execution paths are touched but changes are largely mechanical/spec-driven.

Overview
Switches NitroSQLite null handling to Nitro’s built-in NullType, removing the custom SQLiteNullValue/NITRO_SQLITE_NULL plumbing and making null a first-class SQLiteValue across TS and C++.

Regenerates/renames Nitrogen specs and C++ hybrids (e.g. HybridNitroSQLiteQueryResultSpec), updates execute/executeBatch signatures to use the new types, and adds a native rows getter (NitroSQLiteQueryResultRows) for TypeORM-style access.

Updates the example app to accept the new null behavior (tests use null directly and drop simple-null-handling coverage), tweaks the unit test UI to use FlatList, and relaxes react-native-nitro-modules to * in the example lock/package.

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