[nix] Provide EDA tools through lowrisc-nix mkEdaShell - #2533

• Move to the lowRISC-recommended way of getting EDA tools (README-eda.md), which replaces nix shell lowrisc-it#<tool>. Tool paths and licenses come from $LOWRISC_EDA_CONFIG at runtime, and the flake only declares which tools and versions are needed.
• Bump lowrisc-nix to f351b907, the same revision OpenTitan uses, to get mkEdaShell.
• Add nix/eda_tool_data.json, which lists Xcelium, vManager, Jasper and VCS, using the same versions as OpenTitan.
• Rebuild eda_shell on mkEdaShell and make it the default devShell. nix develop . now drops you into the EDA sandbox in your own shell (bash, fish or zsh).
• Add apps.default and apps.eda_shell, so nix run . -- <cmd> runs a command inside the sandbox.
• A non-hermetic variant that keeps host-installed tools visible is available as nix develop .#eda_shell.nonhermetic.
• Rebuild formal and formal-dev on mkEdaShell with Jasper. They now warn when jg is missing instead of refusing to start. Update dv/formal/README.md to match.
• shell, syn_shell and oss-dev are unchanged, so the formal CI job (which uses oss-dev) is not affected.

Note, I tried the cosim, which worked fine with this. To run jg on my machine, I had to launch it with: jg -allow_unsupported_OS