support using cron expressions for timestamps

[0xphilipp]

This pr will allow some very powerful schedules based on a cron timer. It is only a PoC and if interested I will also adjust the tests to run properly.

It only supports basic crons (with numbers) for performance / gas reasons.

It uses chrono (https://github.com/chronotope/chrono) to convert a unix timestamp to a datetime with components to start the search and convert the result back)

For the search structure the tm structure has been copied: https://docs.rs/mysql/14.0.0/mysql/time/struct.Tm.html

The implementation is based on https://crates.io/crates/crontab with adjustments for weekday support.
This is the major difference to normal cron, that weekdays are complimentary to all other options, which is a lot more sane in my opinion than in the normal implementation. It allows for powerful options like recurring jobs executing exactly first monday of a month (what we will need for our amp governance tune+redelegation)

There is this for blockchains optimized version: https://github.com/CronCats/Schedule
It is a bit more powerful, but not as lightweight as what could be enough for warp.

I feel like the used version is a very clean, straight forward and performant implementation. That is why I always prefer direct integrations for dependencies. Not sure about chrono, but it seems it is okay to run on the chain.

Usage is quite similar to the example in #15

        let result = await context.sdk.createJob(context.accountAddress, {
          condition: {
            expr: {
              uint: {
                left: {
                  // access current_time when executing
                  env: 'time',
                },
                op: 'gt',
                right: {
                  ref: 'next_execution'
                }
              }
            },
          },
          recurring: true,
          requeue_on_evict: true,
          vars: [
            {
              static: {
                kind: 'uint',
                name: 'next_execution',
                value: '1',
                update_fn: {
                  on_error: { ... }
                  on_success: {
                    uint: {
                      env: {
                        // execute 5:00 (0 5) on first - seventh day of a month (1-7), but only on monday (1)
                        // That means execute first monday of a month at 5:00
                        next_time_for_cron: '0 5 1-7 * 1'
                      }
                    },
                  },
                },
              },
            },
          ],
          msgs: [
            {
              wasm: {
                execute: {
                  contract_addr: context.hub,
                  funds: [],
                  msg: base64encode({ harvest: {} }),
                },
              },
            },
          ],
          name: 'eris-harvest',
          reward: '10000',
        });

[simke9445]

What'd be good here is to extract the cron utils to a package (i.e. crontab-plus) and use it as a dependency in warp contracts. More practical in terms of audits.

[0xphilipp]

yes I have thought about that and started doing it. It is deeper nested than expected. If you want I can move everything into the project.