Fix sky light and block light calculation for schematics

[Szabolcs05]

Fix sky light and block light calculation for schematics

Summary
This PR fixes broken lighting when loading schematic files into the world. Previously, lighting was not calculated correctly, resulting in areas being too bright or too dark.

Changes

Sky Light Calculation

• Implemented proper top-down sky light propagation through transparent blocks
• Sky light now correctly stops at opaque blocks and propagates through transparent ones (glass, leaves, flowers, etc.)

Block Light Calculation

• Added support for light-emitting blocks (torches, lanterns, glowstone, etc.)
• Light sources now properly illuminate surrounding areas with correct falloff

Light Propagation

• Implemented flood-fill algorithm for both sky and block light
• Light correctly decreases by 1 for each block traveled through transparent materials

Transparent Block Detection

• Added comprehensive list of transparent block patterns (glass, leaves, flowers, fences, signs, etc.)
• Added list of light-emitting blocks with their respective light levels

Files Changed

• crates/pico_structures/src/world.rs - Global light calculation and propagation
• crates/pico_structures/src/schematic.rs - Transparent/light-emitting block detection
• crates/pico_structures/src/lib.rs - Export LightSection type
• crates/minecraft_packets/src/play/data/light_data.rs - Updated to handle both sky and block light
• crates/minecraft_packets/src/play/chunk_data_and_update_light_packet.rs - Retrieve pre-calculated light data

Result
Schematics now display with natural-looking shadows and proper illumination from light sources.

[Quozul]

This list of string IDs could be handled at compile time, where a build script would map this to smaller and more optimized InternalIds. Same for the LIGHT_EMITTING_BLOCKS const below.
For now, both have manageable amount of strings, so it is relatively fine. Comparing two strings is slower than two integers.

[Quozul]

Don't forget to update the docs to remove the line that says light is not supported.

[Quozul]

Since you are computing the index from the x,y,z coordinates, you could iterate over the index directly, to have only one loop. Similar below for the block_light_volume computation and at other places.

You could also probably merge both loops.

[Szabolcs05]

The sky light loop needs to iterate top-down per column (to track when light gets blocked), so it can't be fully merged with block light. But I can simplify by iterating over columns and merging the inner work.