feat: unify hosted ABI with reusable ASL runtime

[jiale-wangOwO]

Summary

This PR is stacked on #2 at its current head 0fcb5c6. It
keeps #2 as the single hosted entry and preserves its verified ELF sidecars,
versioned C ABI, lock/identity checks, manifest, result handling, and
ExecuteNextPTOInstruction runner.

It adds the reusable runtime layer that was missing from #2:

• neutral ELF ProgramImage/segment contracts and checked loader integration;
• sparse guest memory with permissions, BSS, stack banks, host-memory bridge,
  and atomic instruction transactions;
• versioned architectural state, execution results, snapshots, deterministic
  serialization and hashes;
• process and persistent ASLRef sessions with reset/snapshot lifecycle;
• ASL-owned ELF stepping and a PE-aware runner with explicit completion and
  control-flow policies;
• backend seams for the future native C++ implementation and differential
  comparison;
• package path/bootstrap helpers, runtime documentation, tests, tools, and the
  checked smoke ELF fixture.

These modules do not implement a second PTO decoder or instruction handler.
The ASLRef backend remains the only semantic implementation; ASL continues to
define instruction legality, state changes, faults, and fetch/step behavior.
The existing pto_model_run_elf() ABI from #2 remains the consumer-facing C
entry.

Dependencies

• Must be reviewed after and on top of #2.
• The ASL-owned next-step implementation is aligned with
  PTO-ISA/pto-spec#188; this
  PR does not modify pto-spec.
• Downstream gfrun integration should consume the merged model entry and must
  not restore a separate PTO semantic implementation.

Validation

• Python unit/integration suite: 69 tests run, 61 passed, 8 optional
  external-environment tests skipped
• CMake Release build with -Wall -Wextra -Werror: passed
• CTest: 3/3 passed
• python3 -m compileall: passed
• git diff --check: passed

The branch was rebased onto #2 head 0fcb5c6; no pto-spec files are changed.

[jiale-wangOwO]

Update after exact-head integration check:

• Added commit 02b2bdb to accept current PTO-SPEC#188 artifacts without requiring the temporary PTO_MODEL_* config family.
• Added commit 08d9159 to fix the ASL length subtype in the worker wrapper.
• The merged package keeps pto_model_run_elf() as the only hosted entry and uses ExecuteNextPTOInstruction for current artifacts.
• CMake/CTest and the Python suite pass on the stacked branch.

The current PR188 reference profile still intentionally bounds the reference byte array. High-address/external physical-memory execution is isolated in PTO-SPEC#190; the model does not silently bypass that architectural profile. Full corpus/sidecar scaling remains issue #3.

[jiale-wangOwO]

Additional follow-up commits on the stacked branch:

• 08d9159 fixes the ASL length subtype in the worker wrapper.
• 7c68fa5 fixes standalone package/tool path names after the package rename.

Validation after these commits:

• Python suite: 63 tests collected, 55 passed and 8 environment-dependent tests skipped in the clean contribution worktree.
• CMake Release build and CTest: 3/3 passed.
• compileall and git diff --check: passed.

A test against the clean PTO-SPEC#188 artifact also confirmed that the old profile config family is no longer required. The default reference profile intentionally retains its configured memory bound; external/high-address execution remains the separate #190/#3 scope.

[jiale-wangOwO]

This is the migration of the standalone prototype currently published at https://github.com/jiale-wangOwO/asl-model. It is intentionally based on #2 instead of replacing #2: the public C ABI and runner remain stable, while the richer runtime is folded into the same package. The personal prototype should not be treated as a second implementation after this stacked PR is reviewed.

[jiale-wangOwO]

Cross-repository decisions and merge order are now tracked in Issue #7. This PR remains the runtime extension stacked on #2 and must be reviewed after the base interface is accepted.