fix(scripts): parse the registration id without ggrep

[Dusk1e]

register-validator.sh reads the registration id out of the forge output with ggrep -oP. ggrep is Homebrew's GNU grep: it isn't in the brew install line in the README, and on Linux it doesn't exist at all, so on a machine set up from the docs the command isn't found.

It doesn't stop there either. export VAR=$(...) returns the status of export rather than of the substitution, so set -e never fires. The script carries on with an empty REGISTRATION_ID through configureController(), activateValidator() and updateVotingPower(), and exits 0:

scripts/register-validator.sh: line 53: ggrep: command not found
Registered validator with registration id:
Updating voting power to 20
$ echo $?
0

With the change the id parses normally, and when it genuinely can't be read the script prints the output it got and exits 1 instead of carrying on.

The replacement is POSIX sed against the same _registrationId: uint256 <n> line forge prints under == Return ==, so it matches what -oP ... \K matched, and tail -1 is unchanged. export stays because the Solidity script reads the value through vm.envUint.

[ZhiyuCircle]

Hi @Dusk1e,

Thank you for your interest in contributing to Arc Node, and apologies for the delay in getting back to this PR.

We're closing out the pull request backlog that predates our current contribution policy. This PR is being closed because it does not reference a GitHub issue. All PRs must reference an existing issue using the format Closes: #XXX, and the author must be assigned to that issue before the PR is opened.

This is not a judgement on the change itself. If you'd still like to land it:

1. Open an issue describing the problem, or find the existing one
2. Comment on the issue requesting assignment, and wait for maintainer approval
3. Open a fresh PR once you have been assigned

Please see CONTRIBUTING.md for details. Thanks again for taking the time to contribute.