fix: resolve latest codecheck findings in ptoas and ptobc

[jimmychou0]

Summary

Resolve the latest codecheck scan for tools/ptoas and tools/ptobc (41 findings: 36 fixed, 5 not-applicable with reasons) and fix the CI duplication findings across the split ptoas TUs. Rebased cleanly onto the current main (75e4a22) — replaces the closed #1462; base moved from main to master (new default branch).

• G.CNS.03 — const-ify the five pure Encoder::encode*Immediate helpers (CmpPredicate/Event/MakeTensorView/PartitionView/AllocTile); encodeConstantImmediate still mutates file via internType and stays non-const.
• G.INC.02 — drop 11 redundant includes across ptoas.cpp / ptoas_pipeline.cpp / ptoas_cpp_rewrite.cpp / ptoas_name_hints.cpp.
• G.EXP.27 / G.EXP.36 — if (info.has_variant_u8) → != 0; unsigned += bool counters → explicit if { ++n; }; int hex operand explicitly cast to unsigned before |.
• SecK_MemoryAndResourceLeakChecker — the decoded mlir::Block is owned by std::unique_ptr until region.push_back, so a mid-decode exception can no longer leak it.
• G.CNS.02 — name the hex-escape length/offset (3/2) and SmallString capacity (128) constants.
• G.FMT.17 / G.CMT.04 — remove the blank line at the start of parseNameHintMarker, the orphan // in the driver job-topology diagram, and the run of blank lines after namespace { in ptoas.cpp.
• Duplication (CI) — the ptoas.cpp split had copied the same ~70-line include list into all four TUs; the 62 includes common to all four now live in ptoas_internal.h and each .cpp keeps only its TU-specific includes (net -232 duplicated lines).

Not applicable: borrowedContext ctor / initializeMLIRContext / getMLIRContext (mutable-by-design semantics), pybind11_init__core (macro-generated), char **argv (C main ABI).

Test plan

• 144 host, LLVM 19.1.7 assert build (GCC 13.3): full build warning-free under -Werror.
• CTest 69/69 (45 PTO/PTODSL + 23 PTOBC + smoke).
• Cross-TU include intersection is now empty except the ptoas_internal.h chain; git diff --check clean.