Add GARI support to decoder CLIs

[arshpreetmaan]

Summary

This PR adds C++ CLI support for consuming the GARI matrix and layout files produced by the Python utilities in #273.

• Add --gari-layout support to Tesseract and Simplex.
• Validate the GARI layout schema, detector counts, detector mapping, and observable counts.
• Map physical detector events from circuits or shot files into the corresponding GARI matrix rows.
• Treat virtual detector rows as zero when constructing decoder shots.
• Use physical-then-virtual detector traversal by default in Tesseract when specified by the layout. Explicit detector-order options continue to override this default.
• Record GARI layout information in the statistics output.

Simplex consumes the detector mapping but does not interpret or change detector ordering.

This is the C++ CLI portion split from the broader implementation previously proposed in #269. The GARI transformation itself remains in the Python utility PR #273.

Example

Using

python src/py/_tesseract_py_util/gari.py \
    --circuit circuit_file.stim \
    --prior xor \
    --out-dir gari_output

which produces:

gari_output/circuit_file_gari_xor.dem
gari_output/circuit_file_gari_xor_layout.json

Tesseract can sample from the original circuit and decode using the GARI matrix:

./bazel-bin/src/tesseract \
    --circuit circuit_file.stim \
    --dem gari_output/circuit_file_gari_xor.dem \
    --gari-layout gari_output/circuit_file_gari_xor_layout.json \
    --sample-num-shots 100 \
    --sample-seed 1234 \
    --threads 1 \
    --pqlimit 1000000 \
    --beam 5 \
    --beam-climbing \
    --print-stats \
    --stats-out gari-stats.json

Detector-order options are intentionally omitted: a physical_then_virtual GARI layout makes Tesseract process the matrix rows in their stored order (recommended). Supplying explicit detector-order options overrides this behavior.