Add experimental eBPF backend and runtime profiles

[OFC-KazzKyy]

Summary

This PR adds the first experimental Pop-to-eBPF path while keeping HIR/MIR backend-neutral and making runtime eligibility explicit.

• Add bpfel-unknown-none / bpfeb-unknown-none targets and an LLVM BPF/XDP object-emission path.
• Introduce explicit runtime profiles plus MIR-derived runtime-contract validation, so PLRI remains a contract layer rather than a mandatory runtime implementation.
• Require --runtime-profile linux-ebpf for BPF builds and report missing runtime contracts separately from eBPF verifier/backend restrictions.
• Update ADR 0070, backend architecture docs, diagnostics, CLI coverage, examples, and eBPF validation tests.
• Rebase onto current upstream/master and resolve upstream architecture-contract collisions by renumbering the newly introduced native runtime ADRs to 0071/0072 and removing duplicate public catalog roots.
• Add explicit Rust 1.96 clippy baselines/fixes for existing large compiler modules so the repository keeps a stable -D warnings gate.

Validation

• cargo fmt --all -- --check
• git diff --check upstream/master..HEAD
• PATH=/usr/lib/llvm-22/bin:$PATH LLVM_SYS_221_PREFIX=/usr/lib/llvm-22 cargo check --workspace --all-targets
• PATH=/usr/lib/llvm-22/bin:$PATH LLVM_SYS_221_PREFIX=/usr/lib/llvm-22 cargo clippy --workspace --all-targets -- -D warnings
• PATH=/usr/lib/llvm-22/bin:$PATH LLVM_SYS_221_PREFIX=/usr/lib/llvm-22 cargo test -p pop-architecture-tests
• PATH=/usr/lib/llvm-22/bin:$PATH LLVM_SYS_221_PREFIX=/usr/lib/llvm-22 cargo test --workspace --all-targets

Notes

The PR is intentionally kept as one commit: 59a2e49 Add experimental eBPF backend and runtime profiles.

[kleeedolinux]

profissionalismo gente

[OFC-KazzKyy]

Updated the PR to a single rebased commit with a professional title and description.

Changes in this revision:

• rebased onto current upstream/master;
• fixed the architecture-test blockers from duplicate ADR identities and duplicate public catalog roots;
• kept the eBPF/runtime-profile work in one focused commit;
• re-ran the local workflow-equivalent validation, including fmt, diff --check, check, clippy -D warnings, architecture tests, and full workspace tests.

The latest GitHub Actions run for commit 59a2e49 is waiting for maintainer approval before it can execute.