feat: Improve the extensibility of Hono's Context

[sor4chi]

What is the feature you are proposing?

Currently, Hono's Context is instantiated internally within HonoBase.

By allowing the Context to be injected into HonoBase externally, third-party libraries could freely provide Hono objects with an extended Context.

hono/src/hono-base.ts

Lines 411 to 417 in f9a23a9

	const c = new Context(request, {
	path,
	matchResult,
	env,
	executionCtx,
	notFoundHandler: this.notFoundHandler,
	})

Pros

• Easier to extend
• Enhances the purity of HonoBase

Cons

• Potential for unintended usage
• Could lead to breaking changes

Background

Hono's Context has become bloated over time as new features have been added with each version update.
Since fields included in the Context are not tree-shakable, efforts like #1846 have been made to reduce the weight of the Context.

If we implemented extensible Contexts, we could provide various presets built on top of a minimal Context, allowing users to select only the necessary fields according to their specific use case.

[yusukebe]

I have some ideas. I'll share them later.