[feat] Reentrancy Guard

[drspacemn]

Implement a reentrency guard for the Appchain contract.

References

https://github.com/OpenZeppelin/cairo-contracts/blob/main/src/security/reentrancyguard.cairo

[Akashneelesh]

Heyy @drspacemn may I take this one.

[estheroche]

i am iinterested in this , please can you assign to me?

[glihm]

i am iinterested in this , please can you assign to me?

Hey! Thank you for considering contributing.
A PR is already open for that I'm sorry we forgot to actualise the issue assignment.

Don't hesitate to pick an other one, thank you!

[estheroche]

its fine. thank you