chore: upgrade OpenSSL to 3.6.0 but keep 3.1.2 for FIPS crypto provider

[Manuthor]

The goal of this PR is to upgrade OpenSSL to 3.6.0 but keep official FIPS 3.1.2 version on FIPS mode.

Summary:

OpenSSL Linkage	FIPS	Non‑FIPS
Static	Linkage: OpenSSL 3.6.0; runtime loads FIPS provider from OpenSSL 3.1.2	Linkage: OpenSSL 3.6.0; runtime uses default/legacy providers
Dynamic	Linkage: OpenSSL 3.1.2; ships FIPS configs and provider OpenSSL 3.1.2	Linkage: OpenSSL 3.6.0; ships libssl/libcrypto and providers

• OpenSSL upgrade + packaging plumbing
  • Upgrades OpenSSL to 3.6.0 while keeping 3.1.2 for the FIPS provider.
  • Touches: build.rs, Cargo.toml, openssl.nix, kms-server.nix, shell.nix, default.nix, docker.nix, vcpkg.json, vcpkg_fips.json.
• CI / scripts restructure
  • Changes in .github/scripts/*:
    • refactor smoke tests - removing duplicated tests (add smoke_test_linux.sh, updates to smoke_test_{deb,rpm,dmg}.sh)
    • update_hashes.sh: Nix hashes are retrieved from last CI failure
  • Workflow tweaks: .github/workflows/{packaging.yml,pr.yml,main_base.yml}.
• HSM test stabilization
  • Updates HSM scripts: .github/scripts/test_hsm_{proteccio,utimaco,softhsm2}.sh (and related).
  • Fixes Google CSE HSM verification test: using_hsm.rs.
• Docs / metadata + SBOM
  • README reorg: README.md
  • Regenerated SBOM artifacts with new OpenSSL version: sbom/openssl/, sbom/server/

[serene-kitfisto-8899]

Looks good to me.