🎁 [Feature Request]: feature flags to reduce compiled contract size

[brozorec]

What is the feature you would like to see?

Introduce feature flags in stellar-tokens, stellar-access, and stellar-contract-utils to allow developers to compile only the modules they need, reducing final contract binary size.

Motivation

When we consolidated ~17 separate crates into grouped modules, we optimized for developer experience but increased contract sizes. For example, stellar-tokens now includes code for fungible, non-fungible, vaults, and RWAs even if a project only needs one.

Proposed Solution

Add Cargo feature flags to the following crates:

1. stellar-tokens

• fungible
• non-fungible
• vaults
• rwa

2. stellar-access

• ownable
• roles

3. stellar-contract-utils

• crypto
• math
• merkle-distributor
• pausable
• upgradeable

Usage Example

[dependencies]
stellar-tokens = { version = "x.y.z", default-features = false, features = ["non-fungible"] }

Additional Considerations

• Decide on default features (for backward compatibility?)
• Update documentation with feature flag usage
• Consider inter-crate dependencies (e.g. if rwa depends on fungible)

[brozorec]

this will be fixed with
stellar/rs-soroban-sdk#1672
stellar/stellar-cli#2353