Opening a named partition starts transactions before being able to specify the default timeout and retry limit

[KrzysFR]

Currently, the way to specify default timeout and retry limit settings is to set them on a IFdbDatabase instance, and they will be automatically used by all transactions created from this database instance.

When using the Fdb.OpenNamedPartitionAsync(...) method to create a database instance, you have to wait for the method to complete to get back the db instance and configure it. The problem is that this method need to start a few transactions to read the root subspace prefix from the Directory Layer, which means that it will use the defaults timeout settings (infinite). If the database is not started (or unavailable), then OpenNamedPartitionAsync(..) will not return until either the db goes online, or the CancellationToken passed to it fires (or never if it was CancellationToken.None).

We need a way to pass the various settings to the OpenAsync(...) and OpenNamedPartitionAsync(...) so that they can use them.

Something like

var settings = new FdbConnectionSettings
{
    ClusterFile = @".....",
    DbName = "DB",
    DefaultTimeout = 60 * 1000,
    DefaultRetryLimit = 10,
    // ... more settings to come in future versions?
}
var db = await Fdb.OpenNamedPartitionAsync(settings, someGlobalCancellationToken);
// db.DefaultTimeout => 60000
// db.DefaultRetryLimit => 10

[KrzysFR]

I changed the code to be able to specify default timeout/retry limits, AND open a named partition in a single call to Fdb.OpenAsync(...).

Sample code that opens the named partition ("Foo", "Bar") with a default timeout of 30 sec.

var options = new FdbConnectionOptions()
{
    ClusterFiler = "....", // null for default path
    DefaultTimeout = TimeSpan.FromSeconds(30), // 0 for infinite timeout (default)
    PartitionPath = new [] { "Foo", "Bar" }, // or no partition if null
    // other settings
}
var db = await Fdb.OpenAsync(options, ct);
// opens the database, and switch to the named partitions automatically
// will abort after 30sec if db is not available

This means that Fdb.Directory.OpenNamedPartitions(...) is now obsolete (Fdb.OpenAsync(FdbConnectionOptions, ...) can do the same job).