Implement column aliases in C# and Rust modules

We'd like to be able to do something like this:

// We're using this table as a singleton, so in this table
// there only be one element where the `id` is 0.
[Table(Name = "config", Public = true)]
public partial struct Config
{
    [PrimaryKey]
    [Column(Name = "id")]
    public uint Id;
    [Column(Name = "world_size")]
    public ulong WorldSize;
}

// We're using this table as a singleton, so in this table
// there only be one element where the `id` is 0.
#[spacetimedb::table(name = config, public)]
pub struct Config {
    #[primary_key]
    pub id: u32,
    #[column(name = "foobar")]
    pub foobar: u64,
}

Exactly spelling not proposed. Needs design work. This is a common feature in ORMs:

https://orm.drizzle.team/docs/sql-schema-declaration#tables-and-columns-declaration

Start by comparing the C# and Rust table and column attribute examples in the issue, then review the linked ORM reference for naming conventions. Define the alias behavior and syntax before implementation; done means both modules can map a field name to a different database column name, with the final design documented and tested.