Add CancellationToken support to prompts

[shibayan]

Closes #208

Summary

Prompts can now be canceled from code with a CancellationToken, e.g. to close a pending prompt when the host hides its console, when a request arrives from a server, or on a timeout.

using var cts = new CancellationTokenSource(TimeSpan.FromSeconds(30));

var name = Prompt.Input<string>(options => options.Message = "What's your name?", cts.Token);
var model = Prompt.Bind<MyFormModel>(cts.Token);

API (additive, no breaking changes)

• New overloads taking CancellationToken for the options-object and configure-delegate forms of Input / Password / Confirm / Select / MultiSelect / List, plus Bind<T>(CancellationToken) and Bind<T>(T, CancellationToken).
• Existing signatures are untouched, so this is binary compatible for 3.x. The simple parameter overloads (Input<T>(string message, ...)) were intentionally left alone: adding an optional token there would make the existing overloads ambiguous or break binary compatibility.
• New ModelBinderRegistry.Register<T>(Action<T, CancellationToken>); the existing Register<T>(Action<T>) still works and ignores the token.

Behavior

• When the token is canceled while waiting for input, the prompt is closed the same way as Ctrl+C and an OperationCanceledException (carrying the token) is thrown, independent of ThrowExceptionOnCancel.
• An already-canceled token throws before anything is rendered.
• Console.ReadKey cannot be interrupted, so only when a cancelable token is supplied the form polls KeyAvailable (waiting on the token's wait handle for 16 ms between checks). Without a token, the blocking ReadKey path is unchanged. IConsoleDriver is unchanged.

Source generator

The generated binders now register (model, cancellationToken) => ... and pass the token to each prompt call.

Docs

Added a "Canceling from code" section (en / ja) and a README snippet. Also corrected the existing text that said Ctrl+C returns the default value; it actually exits the process (via Environment.Exit(1)) unless ThrowExceptionOnCancel is set.

Tests

• Form tests: already-canceled token (nothing rendered, no keys consumed), cancellation while waiting for input, and a cancelable but uncanceled token still returning input.
• Registry / Bind tests: both Register overloads, null checks, and Bind passing the token to the binder.
• xUnit1051 is suppressed in the test project: forms under test read from FakeConsoleDriver, which never blocks.
• Full suite passes (682 tests, net8.0 / net10.0).
• Manually verified with DefaultConsoleDriver in a real console window: cancellation fires within ~10 ms of the deadline across consecutive prompts, the next prompt renders below the canceled one, TreatControlCAsInput is restored, and the generated binder for a [PromptBindable] model receives the token.

🤖 Generated with Claude Code

[Copilot]

Copilot review overview

🟡 Changes recommended

The cancellation test relies on a short wall-clock delay and can fail under scheduling stalls.

Review effort: Balanced
Findings: 1

Open (1)

• Make cancellation test deterministic instead of timing-dependent · New

What changed in this PR

Adds CancellationToken support throughout prompt execution and generated model binders.

Changes:

• Adds cancelable prompt and binding overloads.
• Polls console input while observing cancellation.
• Adds tests and English/Japanese documentation.

File	Description
README.md	Adds cancellation example.
docs/​en/​configuration.md	Documents cancellation behavior.
docs/​ja/​configuration.md	Adds Japanese cancellation documentation.
src/​Sharprompt/​Forms/​FormBase.cs	Implements cancellation-aware input polling.
src/​Sharprompt/​ModelBinderRegistry.cs	Supports token-aware binders.
src/​Sharprompt/​Prompt.Basic.cs	Adds token overloads for prompts.
src/​Sharprompt/​Prompt.Bind.cs	Passes tokens to model binders.
src/​Sharprompt.SourceGenerator/​PromptBindableGenerator.cs	Propagates tokens in generated binders.
tests/​Sharprompt.Tests/​Binding/​ModelBinderRegistryTests.cs	Tests binder token propagation.
tests/​Sharprompt.Tests/​Forms/​FormInteractionTests.cs	Tests form cancellation behavior.
tests/​Sharprompt.Tests/​Sharprompt.Tests.csproj	Suppresses the cancellation-token analyzer warning.

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[Copilot]

Copilot review overview

🟢 Approval recommended

Cancellation is consistently propagated, preserves existing behavior, and is covered by deterministic tests and documentation.

Review effort: Balanced
Findings: None

Resolved since last review (1)

• Make cancellation test deterministic instead of timing-dependent