refactor(bevy_inventory): rename plugin and feature-gate snapshot

[h0lybyte]

Summary

• Rename directory bevy_kbve_inventory → bevy_inventory for standalone crates.io readiness
• Feature-gate the JSON snapshot system behind optional snapshot feature (enabled by default)
• Consumers can use default-features = false to drop serde_json if they don't need cross-boundary reads
• All 83 tests pass, compiles with and without snapshot feature

Test plan

• cargo check -p bevy_inventory (with default features)
• cargo check -p bevy_inventory --no-default-features (without snapshot)
• cargo test -p bevy_inventory (69 unit + 14 doc tests)
• cargo check -p isometric-game (workspace still compiles)

[github-actions]

Dependency Review

The following issues were found:

• ✅ 0 vulnerable package(s)
• ✅ 0 package(s) with incompatible licenses
• ✅ 0 package(s) with invalid SPDX license definitions
• ⚠️ 3 package(s) with unknown licenses.

See the Details below.

License Issues

packages/rust/bevy/bevy_inventory/Cargo.toml

Package	Version	License	Issue Type
bevy	>= 0.18.0, < 0.19.0	Null	Unknown License
serde	>= 1.0.0, < 2.0.0	Null	Unknown License
serde_json	>= 1.0.0, < 2.0.0	Null	Unknown License

OpenSSF Scorecard

Package	Version	Score	Details
cargo/bevy	>= 0.18.0, < 0.19.0	Unknown	Unknown
cargo/serde	>= 1.0.0, < 2.0.0	Unknown	Unknown
cargo/serde_json	>= 1.0.0, < 2.0.0	Unknown	Unknown

Scanned Files

• packages/rust/bevy/bevy_inventory/Cargo.toml
• packages/rust/bevy/bevy_kbve_inventory/Cargo.toml