support readdir in batch

[DoubleSpout]

When using etcd's cli:readdir, if the value in this path is too large (by default: exceeding 4MB), you will encounter the

following error:

rpc error: code = ResourceExhausted desc = grpc: received message larger than max (8653851 vs. 4194304).

Therefore, we need to read this directory in batches.

local cli, _ = etcd.new([option:table])

local res, err
local start_key = '/path/to/dir'
local last_key = start_key
local range_end = cli.rangeend(start_key)
local data = {}
while(1) do
    res, err = cli:readdir(last_key, {
        timeout = 3000,
        range_end = range_end,
        revision = -1,
        limit = 20, -- batch size 
        sort_order = 'ASCEND',
        sort_target = 'KEY',
    })
    -- error handle
    if err or not res then
        break
    end
    -- collect res.body
    table.insert(data, res.body)
    local last_kv_key = res.body.kvs[#res.body.kvs].key
    last_key = cli.nextkey(last_key)
    if not res.body.more then
        break
    end
end

for _, body in ipairs(data) do
    -- handle data
end

This commit also fixes some testing bugs in continuous integration, update ci image from ubuntu-20.04 to ubuntu-22.04.

[DoubleSpout]

GitHub Actions has deprecated the Ubuntu 20.04 runner image ( ubuntu-20.04 ). The deprecation process began on February 1, 2025, and the image became fully unsupported on April 1, 2025.
This means that workflows in GitHub Actions using runs-on: ubuntu-20.04 will no longer be officially supported and may experience failures or unexpected behavior.
Reason for Deprecation:
The deprecation of ubuntu-20.04 is a standard practice as newer Long Term Support (LTS) versions of Ubuntu are released and become available as runner images (e.g., ubuntu-22.04, ubuntu-24.04). This ensures that the GitHub Actions environment remains up-to-date, secure, and compatible with the latest software and dependencies.
Action Required:
Users with workflows still utilizing ubuntu-20.04 are advised to migrate to a newer supported Ubuntu runner image, such as ubuntu-latest, ubuntu-22.04, or ubuntu-24.04, to ensure the continued functionality and stability of their CI/CD pipelines.