[schema] introduce module

[fwbrasil]

From the module's README:

kyo-schema

Define a case class and get JSON serialization, Protobuf encoding, field validation, type-safe lenses, structural diffs, and more, all derived from the type's structure. No annotations, no boilerplate. Works across JVM, JavaScript, and Scala Native.

The module depends only on kyo-data (pure data structures) and has no dependency on Kyo's effect runtime, so it can be adopted as a standalone library.

// Schema-based JSON and Protobuf
Json.encode(alice)      // {"id":1,"name":"Alice","password":"secret","address":{"city":"Portland","zip":"97201"}}
Protobuf.encode(alice)  // Span[Byte] (binary)

// Type-safe lenses reach any depth
Schema[User].focus(_.address.city).update(alice)(_.toUpperCase)
// User(1, "Alice", "secret", Address("PORTLAND", "97201"))

// Type-level reshaping: drop sensitive fields, rename, add computed
val publicView = Schema[User]
    .drop(_.password)
    .rename(_.name, "displayName")
// Encodes alice as: {"id":1,"displayName":"Alice","address":{"city":"Portland","zip":"97201"}}

// Diffs as data: capture just what changed, ship, replay
val renamed = alice.copy(name = "Alicia")
val cs = Changeset(alice, renamed) // Produces a changeset with the new name patch
cs.applyTo(alice)                  // Result.Success(renamed)

Everything flows from Schema[A], the central type that captures a type's structure at compile time. It's the single source of truth that powers serialization, validation, navigation, and conversion.

The module provides these primitives:

Primitive	Purpose
Json / Protobuf	Serialize to JSON strings or Protocol Buffers bytes
Focus	Type-safe lens for reading, writing, and modifying fields at any depth
Compare	Read-only field-by-field comparison of two values
Modify	Batched field mutations applied as a single unit
Changeset	Serializable diff that can be stored, transmitted, and replayed
Builder	Incremental, type-safe case class construction
Convert	Bidirectional conversion between structurally compatible types
Structure	Runtime type description and untyped value trees