Update new option binding handling

[alzimmermsft]

What does this PR do?

Updates new option binding handling with the following updates:

• Add support for Aliases when binding command-line options.
• Add support for DefaultValue when binding command-line options.
• Replaced Dictionary lookup for handling with more flexible OptionTypeHandler.CreateFromDescriptor. This better supports string? and arity handling.
• Cache OptionTypeHandlers for each TOption processed as Options are handled in a way where they aren't mutated once created.
• Added new extension methods for new binding pattern as we no longer need to deal with side-effect modifications to Option with when changing requiredness that existed in the old binding pattern.

GitHub issue number?

[Link to the GitHub issue this PR addresses]

Pre-merge Checklist

• Required for All PRs
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  • Updated servers/Azure.Mcp.Server/README.md and/or servers/Fabric.Mcp.Server/README.md documentation
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• Extra steps for Azure MCP Server tool changes:
  • Updated command list in servers/Azure.Mcp.Server/docs/azmcp-commands.md
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[Copilot]

⚠️ Not ready to approve

The new OptionTypeHandler has critical correctness issues (enum multi-value binding type mismatch and unsafe IEnumerable element-type extraction) and alias support lacks regression tests.

Pull request overview

This PR refactors the core option-binding pipeline used by commands to improve option creation/binding flexibility (notably adding alias support), moving from a type-handler dictionary to descriptor-driven OptionTypeHandler creation with caching.

Changes:

• Introduces OptionTypeHandler to create System.CommandLine.Option instances from OptionDescriptor (including support for Aliases) and bind values via option-instance lookup.
• Updates option descriptor and binder behavior to better account for nullability and multi-value arity, and removes the old enum validator helper in favor of in-handler validation.
• Adjusts related extensions/docs and adopts primary constructor usage in one command base class.

File summaries

File	Description
core/Microsoft.Mcp.Core/tests/Microsoft.Mcp.Core.Tests/Options/OptionBinderTests.cs	Updates array arity expectation in unit tests (nullable array now treated as ZeroOrMore).
core/Microsoft.Mcp.Core/src/Options/OptionTypeHandler.cs	Adds the new descriptor-driven option creation/binding implementation (including aliases, nullability/multi-value handling, enum validation).
core/Microsoft.Mcp.Core/src/Options/OptionNameConvention.cs	Moves the type into the Options namespace and minor formatting.
core/Microsoft.Mcp.Core/src/Options/OptionDescriptor.cs	Makes Description required, adds Aliases, and updates descriptor creation from [Option].
core/Microsoft.Mcp.Core/src/Options/OptionBinder.cs	Switches to cached OptionTypeHandler[] per options type for registration and binding.
core/Microsoft.Mcp.Core/src/Options/OptionAttribute.cs	Adds Aliases to the attribute contract.
core/Microsoft.Mcp.Core/src/Options/EnumOptionValidator.cs	Removes the prior enum option validator helper (logic moved into OptionTypeHandler).
core/Microsoft.Mcp.Core/src/Extensions/ParseResultExtensions.cs	Adds an internal option-instance-based getter helper for the new binding approach.
core/Microsoft.Mcp.Core/src/Extensions/CommandResultExtensions.cs	Adds a matching internal option-instance-based getter helper for the new binding approach.
core/Microsoft.Mcp.Core/src/Commands/BaseCommand`2.cs	Adds XML doc comments for option validation hook.
core/Azure.Mcp.Core/src/Commands/Subscription/SubscriptionCommand`2.cs	Converts to a primary constructor and simplifies field initialization.

Copilot's findings

• Files reviewed: 11/11 changed files
• Comments generated: 11

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