fix: unnecessary mut on processed_count and unused variable now in lib.rs

[Pvsaint]

Problem

Two Clippy warnings in lib.rs block CI:

warning: variable does not need to be mutable
    --> fluxapay/src/lib.rs:1278:13
     |
1278 |         let mut processed_count = 0u32;

warning: unused variable: `now`
    --> fluxapay/src/lib.rs:1277:13
     |
1277 |         let now = env.ledger().timestamp();

processed_count is never mutated after declaration, and now is assigned but never read.

Acceptance Criteria

• mut is removed from processed_count declaration if it is truly never mutated, or the variable is used correctly in loop logic
• now is either removed (if unused) or used in expiry/timing logic as intended
• If now and processed_count reveal incomplete logic (e.g. a batch processor stub), a TODO comment documents the intent
• cargo clippy --all-targets --all-features -- -D warnings passes

Branch & Commit Examples

branch: fix/clippy-warnings-cleanup
commit: fix(lib): remove unnecessary mut and unused now variable in batch processor