P19 expands the official RV32I pass set

P19 widens P18 from four official tests to twelve.

Command:

make -C projects/19_rv32i_imm_alu_tests/test

Result: PASS

group	tests
Existing P18 passes	`I-nop-00.S`, `I-fence-00.S`, `I-lui-00.S`, `I-addi-00.S`
New immediate ALU passes	`I-ori-00.S`, `I-andi-00.S`, `I-xori-00.S`, `I-slti-00.S`, `I-sltiu-00.S`, `I-slli-00.S`, `I-srli-00.S`, `I-srai-00.S`

The runner still is not a full reference-model flow. It now has a source-level signature generator for generated immediate-ALU tests. That is enough to keep this honest without pretending the whole upstream suite passes.

The next tests to try are AUIPC and the R-type ALU group.