Serialize sierra version to int not string

[maciektr]

Serialize sierra version field to int instead of string (i.e. version = 1 instead of version = "1".
For context on serde side see: serde-rs/serde#745

This change is 

[mkaput]

Reviewed 3 of 3 files at r1, all commit messages.
Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @maciektr and @orizi)

a discussion (no related file):
We'd like to land this change before 2.3.0-rc2 is released because technically this is breaking.

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crates/cairo-lang-sierra/src/program.rs line 41 at r1 (raw file):

#[derive(Debug, Error)]
#[error("Invalid version")]

Unsupported Sierra program version

Code quote:

Invalid version

[maciektr]

Reviewable status: 2 of 3 files reviewed, 2 unresolved discussions (waiting on @mkaput and @orizi)

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crates/cairo-lang-sierra/src/program.rs line 41 at r1 (raw file):

Previously, mkaput (Marek Kaput) wrote…

Unsupported Sierra program version

Done.

[mkaput]

Reviewed 1 of 1 files at r2, all commit messages.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @maciektr and @orizi)

[orizi]

Reviewed all commit messages.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @maciektr)