math.big: fix `a + b` and `a - b`, when the signs are different, add more test cases #11120

	name: vlib modules CI

	on:
	pull_request:
	paths:
	- 'vlib/**.v'
	- 'vlib/**.md'
	- 'cmd/tools/vdoc/**.v'
	- '**/module_docs_ci.yml'
	push:
	paths:
	- 'vlib/**.v'
	- 'vlib/**.md'
	- 'cmd/tools/vdoc/**.v'
	- '**/module_docs_ci.yml'

	# Allow only one concurrent deployment, skipping runs queued between the run in-progress and latest queued.
	# However, do NOT cancel in-progress runs as we want to allow these production deployments to complete.
	concurrency:
	group: ${{ github.workflow }}-${{ github.ref }}
	cancel-in-progress: ${{ !contains(github.ref, 'master')}}

	jobs:
	build-module-docs:
	runs-on: ubuntu-20.04
	steps:
	- uses: actions/checkout@v4
	- name: Build V
	run: make -j4 && ./v symlink
	- name: Install markdown from vpm
	run: v retry -- v install markdown
	- name: Test v doc
	run: ./v test cmd/tools/vdoc/
	- name: Build module documentation
	run: ./v doc -m -f html vlib/
	- name: Deploy docs to vercel
	if: github.event_name == 'push' && github.repository == 'vlang/v' && github.ref == 'refs/heads/master'
	run: npx vercel --confirm --prod --name vmodules --token ${{ secrets.VERCEL_TOKEN }} vlib/_docs/ \|\| true

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