Add temporal range types and reusable options groups

[carldebilly]

Why

Two recurring pain points when building CLI apps with Repl Toolkit:

1. Repeated option sets — commands that share the same options (output format, verbosity, pagination…) force developers to duplicate parameters on every handler. This is error-prone and makes it hard to keep option names and aliases consistent across commands.

2. Date/time intervals — querying logs, generating reports, or filtering audit trails almost always requires a "from/to" range. Today this means two separate parameters, manual validation that to >= from, and no compact syntax for "start + duration" patterns.

What changed

Reusable options groups ([ReplOptionsGroup])

A class decorated with [ReplOptionsGroup] can now be used directly as a handler parameter. Its public writable properties are expanded into individual command options, exactly as if they were declared on the handler itself.

[ReplOptionsGroup]
public class OutputOptions
{
    [ReplOption(Aliases = ["-f"])]
    public string Format { get; set; } = "text";

    [ReplOption(ReverseAliases = ["--no-verbose"])]
    public bool Verbose { get; set; }
}

app.Map("list", (OutputOptions output, int limit) => ...);
app.Map("show", (OutputOptions output, string id) => ...);

• PascalCase properties are automatically lowered to camelCase tokens (Format → --format)
• All parameter attributes ([ReplOption], [ReplArgument], [ReplValueAlias]) work on properties
• Property initializer values serve as defaults
• Help text generation fully supports group properties (descriptions, defaults, placeholders)
• Name collisions between group properties and regular parameters are detected at registration
• Nested groups and abstract/interface types are rejected with clear error messages

Temporal range types

Three new record types represent date/time intervals: ReplDateRange, ReplDateTimeRange, and ReplDateTimeOffsetRange. They support two compact literal syntaxes:

• Range: 2024-01-15..2024-02-15
• Duration: 2024-01-15@30d

app.Map("report", (ReplDateRange period) =>
    $"{period.From:yyyy-MM-dd} to {period.To:yyyy-MM-dd}");

Reversed ranges (To < From) produce a validation error. Duration syntax reuses the existing TimeSpanLiteralParser.