fix(demo-rollup): fix assertions' inconsistencies

[YichiZhang0613]

Description

In rollup_coarse_measure.rs, the message indicates tps should be >= MIN_TPS(fail when "below") while the predicates require tps > MIN_TPS. According to const's definition(comments), it should be tps >= MIN_TPS. So the
assert!(tps < MAX_TPS, "TPS {tps} reached unrealistic number {MAX_TPS}, investigation is needed"); should also be changed.

In graceful.rs, the predicate requires slot.number > last_processed_slot_number while the message requires slot.number >= last_processed_slot_number(fail when "is lower than"). The message should be changed.

// Minimum TPS, below which it is considered an issue
const MIN_TPS: f64 = 1000.0;
// Number to check that rollup actually executed some transactions
const MAX_TPS: f64 = 30_000.0;

• [] I have updated CHANGELOG.md with a new entry if my PR makes any breaking changes or fixes a bug. If my PR removes a feature or changes its behavior, I provide help for users on how to migrate to the new behavior.
• [] I have carefully reviewed all my Cargo.toml changes before opening the PRs. (Are all new dependencies necessary? Is any module dependency leaked into the full-node (hint: it shouldn't)?)

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[YichiZhang0613]

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