Update to Chisel 7

[kammoh]

• update to Chisel 7.1.1
• update mill build
• add mill build script to git
• update the Scala version
• update Berkeley softfloat and testfloat submodules
• fix format strings for printfs and scanfs of uint64_t (TODO: would be more portable to use PRIu64 instead of llu/llx)