Issue Fix

[JSE19]

Description
Improves the streaming contract by: (1) clarifying Stream struct field documentation with explicit units and semantics, (2) emitting the computed new_end_time in the top-up event so off-chain consumers know when the stream will drain, and (3) hardening the Rust toolchain by declaring a minimum supported Rust version (1.81.0) with workspace Cargo.toml and README documentation.

Type of Change

• ✨ New feature (non-breaking change which adds functionality)
• 🔧 Refactoring (no functional changes)
• 📚 Documentation update

Changes Made

• contracts/stream_contract/src/types.rs — Rewrote all Stream struct field docs to specify units (stroops, Unix epoch seconds) and clarify when each field is meaningful (e.g. paused_at vs paused)
• contracts/stream_contract/src/events.rs — Added new_end_time: u64 field to StreamToppedUpEvent
• contracts/stream_contract/src/lib.rs — Compute new_end_time during top-up: now + remaining / rate_per_second
• contracts/stream_contract/src/test.rs — Assert new_end_time == 150 in test_top_up_emits_event
• contracts/Cargo.toml — Added rust-version = "1.81.0", documented all profile settings with inline comments
• contracts/stream_contract/Cargo.toml — Added rust-version = "1.81.0"
• contracts/README.md — Added "Rust Toolchain" section explaining CI uses stable + wasm32-unknown-unknown

Testing

• Unit tests added/updated
• Manual testing performed

Test Steps

1. Run cargo test in contracts/ — all tests pass, including new assertion on new_end_time
2. Run cargo build --release — WASM size stays within 200 KB budget

Checklist

• My code follows the project's style guidelines
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

Closes #1009
Closes #1010
Closes #1011