Error without overflow checks

[mootz12]

What

Update checks for Cargo during stellar contract build to throw errors instead of warnings.

Why

Prevent the CLI from being used to build contracts without overflow-checks = true

Known limitations

None

[Copilot]

Pull request overview

This PR converts overflow-checks validation from warnings to errors during stellar contract build, preventing contracts from being built without overflow-checks = true in their Cargo.toml configuration.

Changes:

• Modified run_checks() and check_overflow_checks() functions to return errors instead of emitting warnings
• Added new CargoConfiguration error variant for Cargo.toml validation failures
• Updated all tests to expect errors instead of warnings and verify proper failure/success behavior
• Added overflow-checks = true to the root Cargo.toml's release profile
• Fixed spelling: "retreiving" → "retrieving"

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
cmd/soroban-cli/src/commands/contract/build.rs	Converted overflow-checks validation from warnings to errors; added CargoConfiguration error type; fixed spelling typo
cmd/crates/soroban-test/tests/it/build.rs	Updated test names and assertions to expect errors instead of warnings; adjusted fixture paths to copy entire workspace; added new test cases for various overflow-checks scenarios
Cargo.toml	Added overflow-checks = true to release profile to ensure the CLI itself is built with overflow checks enabled