[feat] Make the openvm::entry! macro a proc-macro attribute

[Golovanov399]

This resolves INT-2784. Now, instead of openvm::entry!(main), we just write #[openvm::entry] before fn main.

[jonathanpwang]

I was wondering, do you think it's safe to add the #![no_main] within the macro, where it figures out based on whether std is enabled etc? This has the benefit that on host we can make it always std and allows cargo clippy to work etc

[jonathanpwang]

Rename suggestion, and wanted to ask/discuss if we can handle no_main within the macro for better UX. Otherwise LGTM

[github-actions]

group	app.proof_time_ms	app.cycles	app.cells_used	leaf.proof_time_ms	leaf.cycles	leaf.cells_used
verify_fibair	(+11 [+0.5%]) 2,186	513,827	18,710,764	-	-	-
fibonacci_program	(-10 [-0.2%]) 5,302	1,500,095	51,485,080	-	-	-
regex_program	(+65 [+0.4%]) 15,281	1,914,103	165,455,373	-	-	-
ecrecover_program	(-70 [-2.7%]) 2,516	284,567	15,055,723	-	-	-

Commit: 521f8af

Benchmark Workflow