[Feature] Organize demos into dedicated crates

[vmarcella]

Overview

Reorganize the existing examples from crates/lambda-rs/examples/ into a
dedicated demos/ directory at the repository root. Demo crates will be
included in the main workspace members but excluded from default-members,
so they are not built by default but remain accessible via -p flag. This
structure enables better feature flag management per demo category, cleaner
build configurations, and a more scalable approach for showcasing engine
capabilities.

Current State

Examples currently reside in crates/lambda-rs/examples/ as individual .rs
files:

crates/lambda-rs/examples/
├── audio_sine_wave.rs
├── immediates.rs
├── indexed_multi_vertex_buffers.rs
├── instanced_quads.rs
├── minimal.rs
├── offscreen_post.rs
├── play_slash_sound.rs
├── reflective_room.rs
├── sound_buffer_load.rs
├── textured_cube.rs
├── textured_quad.rs
├── triangle.rs
├── triangles.rs
└── uniform_buffer_triangle.rs

This flat structure has several limitations:

• All examples share the same Cargo feature configuration
• No separation between audio, rendering, and other demo categories
• Difficult to enable feature flags selectively per demo type
• Examples must be run via cargo run --example <name> -p lambda-rs

Scope

Goals:

• Create a demos/ directory at the repository root
• Organize demos into domain-specific crates (e.g., demos/audio/,
  demos/render/, demos/minimal/)
• Configure appropriate feature flags per demo crate
• Add demo crates to workspace members but exclude from default-members
• Maintain backward compatibility by keeping minimal examples in
  crates/lambda-rs/examples/ for documentation purposes
• Provide clear README documentation for running demos

Non-Goals:

• Creating new demos (existing examples will be migrated)
• Modifying the core lambda-rs or lambda-rs-platform APIs
• Automated demo testing infrastructure (can be addressed separately)

Proposed API

demos/
├── README.md            # Documentation for running demos
├── audio/
│   ├── Cargo.toml       # [features] audio-specific flags
│   └── src/
│       └── bin/
│           ├── sine_wave.rs
│           ├── play_sound.rs
│           └── sound_buffer.rs
├── render/
│   ├── Cargo.toml       # [features] render-validation, etc.
│   └── src/
│       └── bin/
│           ├── triangle.rs
│           ├── triangles.rs
│           ├── immediates.rs
│           ├── indexed_multi_vertex_buffers.rs
│           ├── instanced_quads.rs
│           ├── textured_quad.rs
│           ├── textured_cube.rs
│           ├── uniform_buffer_triangle.rs
│           ├── offscreen_post.rs
│           └── reflective_room.rs
└── minimal/
    ├── Cargo.toml       # Minimal dependencies
    └── src/
        └── bin/
            └── minimal.rs

Example demos/render/Cargo.toml:

[package]
name = "lambda-demos-render"
version = "0.1.0"
edition = "2021"
publish = false

[dependencies]
lambda-rs = { path = "../../crates/lambda-rs" }

[features]
default = []
validation = ["lambda-rs/render-validation"]
validation-strict = ["lambda-rs/render-validation-strict"]

[[bin]]
name = "triangle"
path = "src/bin/triangle.rs"

[[bin]]
name = "textured_quad"
path = "src/bin/textured_quad.rs"

# ... additional binaries

Root Cargo.toml changes:

[workspace]
resolver = "2"

members = [
  "crates/lambda-rs",
  "crates/lambda-rs-args",
  "crates/lambda-rs-logging",
  "crates/lambda-rs-platform",
  "tools/obj_loader",
  "tools/lambda_audio",
  # Demo crates included in workspace but not built by default
  "demos/audio",
  "demos/render",
  "demos/minimal",
]

default-members = [
  "crates/lambda-rs",
  "crates/lambda-rs-args",
  "crates/lambda-rs-logging",
  "crates/lambda-rs-platform",
  "tools/obj_loader",
]

Running demos:

# Run a render demo with default features
cargo run -p lambda-demos-render --bin triangle

# Run with validation enabled
cargo run -p lambda-demos-render --bin triangle --features validation

# Run an audio demo
cargo run -p lambda-demos-audio --bin sine_wave

Acceptance Criteria

Acceptance Criteria

• demos/ directory created at repository root
• demos/audio/ crate with migrated audio examples
• demos/render/ crate with migrated rendering examples
• demos/minimal/ crate with basic window example
• Each demo crate has appropriate feature flags configured
• Root Cargo.toml updated: demo crates added to members, excluded from
  default-members
• cargo build does not build demos by default
• cargo build -p lambda-demos-render builds only the render demos
• demos/README.md documents how to build and run demos
• Existing crates/lambda-rs/examples/ simplified to minimal reference
  examples for rustdoc
• All migrated demos compile and run successfully

Affected Crates

lambda-rs

Notes

• Demo crates should use publish = false to prevent accidental publishing
• Excluding demos from default-members keeps cargo build --workspace fast
  while still allowing cargo build -p <demo-crate> access
• Consider adding a demos/shared/ crate if common utilities emerge
• Feature flags in demo crates should mirror high-level lambda-rs features
• This structure aligns with patterns used in wgpu and bevy repositories
• Future demos (physics, UI, etc.) can follow the same pattern