feat(jstz_engine): add safe wrapper for JS Scripts

[johnyob]

Context

Adds memory and type-safe version of JSScript.

Description

Adds ability to compile and evaluate scripts.

Manually testing the PR

cargo nextest run --package jstz_engine

[codecov]

Codecov Report

Attention: Patch coverage is 67.00000% with 33 lines in your changes missing coverage. Please review.

Project coverage is 45.69%. Comparing base (4d1d373) to head (9106c11).

Files with missing lines	Patch %	Lines
crates/jstz_engine/src/script.rs	67.00%	32 Missing and 1 partial ⚠️

Files with missing lines	Coverage Δ
crates/jstz_engine/src/lib.rs	100.00% <ø> (ø)
crates/jstz_engine/src/script.rs	23.42% <67.00%> (ø)

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