Adding custom entrypoint option for charting

[findolor]

Closes #675

Caution

Do not merge before #887

Motivation

See issue: #675

Solution

• Added entrypoint field to Scenario
• Use the new entrypoint in the fuzzer, fallback to calculate-io and handle-io if does not exist

Checks

By submitting this for review, I'm confirming I've done the following:

• made this PR as small as possible
• unit-tested any new functionality
• linked any relevant issues or PRs

[thedavidmeister]

screenshots and tests?

[findolor]

@thedavidmeister

the tests are here:

rain.orderbook/crates/common/src/fuzz/mod.rs

Line 856 in 7b882ce

async fn test_custom_entrypoint() {

Here is an image of a simple order that contains a scenario with a custom entrypoint and the stack values for that:

[thedavidmeister]

can you please update spec at https://github.com/rainlanguage/specs/blob/main/ob-yaml.md

[findolor]

@thedavidmeister created this PR

[thedavidmeister]

don't merge this yet, because dependant branch is not reviewed