Consolidate GPU runtimes and extend JPEG and HTJ2K validation

[jcwal1516]

Metal runtime initialization is split into lazy decode, encode, profiling and buffer-operation groups with separate shader inputs. A new j2k-mpsgraph-support package owns graph submission lifetime shared with JXR. Compact native encoding reuses checked memory accounting, and obsolete timing fields are deprecated.

This review also includes pending JPEG ICC/transfer-syntax work, bounded HTJ2K candidate rate control, Metal IDWT and resident-encoding changes, benchmark instrumentation, release/API inventory updates, and removal of obsolete execution plans.

Resident lossy HT execution is wired into the tile path, and Classic batching respects the private-allocation cap before submission. The previously failing regressions now pass. Lint fixes retain strict gates, and the core/JPEG/Metal/MPSGraph API inventory changes have explicit reviewed fingerprints and migration rationale; snapshots were regenerated with the canonical tools.

Validation on Apple Silicon macOS:

• J2K_REQUIRE_METAL_RUNTIME=1 RUST_TEST_THREADS=1 cargo test -p j2k-metal --tests --locked: 519 passed, 26 ignored.
• cargo xtask metal-compile, cargo xtask clippy, and cargo xtask clippy-strict: passed.
• cargo xtask semver --write-report: passed, including all pinned compatibility checks.
• cargo xtask stable-api --write, cargo xtask release-integrity, and cargo xtask repo-lint: passed (101 repository-policy tests).
• Formatting, snapshot diff checks and Gitleaks on the new commit: passed.

Exact-head GPU validation passed for CUDA and Metal at commit 8bba69d6f820d8c547c8d5b79f1cd68a904313d6: https://github.com/frames-sg/j2k/actions/runs/33944361504. The unsafe benchmark audit and all four command-orchestration integration tests also pass. All hosted PR checks, including the exact-SHA GPU evidence policy and aggregate required gate, passed after the evidence rerun. Publishing the new shared graph package remains a separate registry-release action.