build(metadata): cleanup project.properties usage

[MattSturgeon]

project.properties is deprecated since Gradle 9.6, for removal in Gradle 10.

Migrate to sc.properties and take advantage of SCElement.to<type>() for simplifying deserialization.

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This approach is blocked by stonecutter#56, because rawOrNull does not include "less specific" properties in the SCElement result:

project.path // ⇒ :forge:1.17.1
sc.properties.rawOrNull("reqs") // ⇒ {mc: ~1.17.1}
sc.properties.rawOrNull("reqs", "cloth") // ⇒ ^5

For these properties:

["1.17.1"]
reqs.cloth = "^5"
reqs.fabric_loader = ">=0.12.11"
reqs.forge_version = ">=37"
reqs.forge_loader = ">=37"
fabric.reqs.mc = "~1.17"
forge.reqs.mc = "~1.17.1"