Add RISC-V 64-bit (riscv64) platform support

[gounthar]

The candidates service does not recognize linuxriscv64 as a platform identifier.

Changes needed

1. Platform.scala: add case for "linuxriscv64" and define val LinuxRISCV64 = Platform("LINUX_RISCV64", "Linux RISC-V 64bit")

Related

• feat: add RISC-V 64-bit platform support sdkman-cli#1496, feat: add RISC-V 64-bit platform support sdkman-cli-native#375, feat: add RISC-V 64-bit platform support sdkman-disco-integration#46, feat: add RISC-V 64-bit (riscv64) platform support vendor-release#17, feat: add RISC-V 64-bit (riscv64) platform support sdkman-broker-2#10

[chloe41427]

Thank you for the contribution! RISC-V platform support is something we'd love to tackle, but it touches many parts of the SDKMAN! ecosystem simultaneously. Before we can take this on properly, we need to complete our ongoing migration to the new sdkman-state API, which will change how platform support works across the board. We'd also ask that any platform additions are discussed on our Discord server first, so we can coordinate the effort together. Closing this for now — we'll revisit RISC-V support once the migration is complete. Thanks for your patience! 🙏