Make Gradle runner resilient to local JDK and remove Foojay plugin

[LMLiam]

Description

• Remove the Foojay toolchains settings plugin from settings.gradle to avoid mandatory plugin resolution during settings evaluation.
• Add support in the processor/annotation code for no-arg @ServiceProvider usage by giving ServiceProvider a default empty value and implementing inferContractsFromProvider in ServiceSchemeProcessor to BFS supertypes and collect @ServiceContract interfaces; emit a clear compilation error when none can be inferred.
• Add unit tests covering no-arg provider inference and the error case in ServiceSchemeProcessorSpec.kt.

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[chatgpt-codex-connector]

Keep a Java 24 toolchain source configured

Removing the Foojay toolchains resolver here means Gradle no longer has any toolchain download repository configured. The modules still request Java 24 toolchains (see modules/annotations/build.gradle and modules/processor/build.gradle), so any environment without a locally installed JDK 24 will now fail toolchain resolution with “no compatible toolchain” instead of provisioning one. If the intent is to avoid network access during settings evaluation, consider an alternative local toolchain repo configuration or lowering the toolchain version to what’s already installed rather than dropping resolver support entirely.

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