Use `IsZero` and "zero" instead of `Nil` and "nil" for pointer-like types (except `arena.Pointer`) #1998

	name: ci
	on:
	push:
	branches: [main]
	tags: ['v*']
	pull_request:
	branches: [main]
	schedule:
	- cron: '15 22 * * *'
	workflow_dispatch: {} # support manual runs
	permissions:
	contents: read
	jobs:
	ci:
	runs-on: ubuntu-latest
	strategy:
	matrix:
	go-version: [1.21.x,1.22.x,1.23.x]
	steps:
	- name: Checkout Code
	uses: actions/checkout@v4
	with:
	fetch-depth: 1
	- name: Install Go
	uses: actions/setup-go@v5
	with:
	go-version: ${{ matrix.go-version }}
	- name: Cache
	uses: actions/cache@v4
	with:
	path: ~/go/pkg/mod
	key: ${{ runner.os }}-protocompile-ci-${{ hashFiles('**/go.sum') }}
	restore-keys: ${{ runner.os }}-protocompile-ci-
	- name: Test
	run: make test
	- name: Benchmarks
	# no need to run benchmarks for every Go version
	if: matrix.go-version == '1.23.x'
	run: make benchmarks
	- name: Lint
	# Often, lint & gofmt guidelines depend on the Go version. To prevent
	# conflicting guidance, run only on the most recent supported version.
	# For the same reason, only check generated code on the most recent
	# supported version.
	if: matrix.go-version == '1.23.x'
	run: make checkgenerate lint

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