Upgrade starknet 2.6.0, Snfoundry 0.26.0

[julienbrs]

closes #85
Updated Scarb to 2.6.0, snfoundry to 0.26.0, which led to changes like start_cheat_caller_address, declare and deploy,... Changes related to events assertions will me made in #111.
Also updated Readme and CI, so tests runs more often

[tekkac]

lgtm

minor notes:

• we might need to keep times, or at least the starting year in a storage var
• scarb version should be gotten from .tool-versions

[julienbrs]

lgtm

minor notes:

• we might need to keep times, or at least the starting year in a storage var
• scarb version should be gotten from .tool-versions

• Starting_year can easily be fetched, it's the year of the first vintage. Do we really need to use a storage var? If we really want a getter, we can create a function that does the fetch and return the .year, what do you think?
• Removed .tool-versions from gitignore