Fix Clippy Errors

[adust09]

• needless_range_loop / needless-range-loop
  Replaced loops that indexed collections with iterator-based patterns (iter_mut() + enumerate() or direct slice fills) to mutate elements without manual indexing.
• collapsible_if
  Flattened nested if let/if chains into single guard-style if let statements, keeping control flow intact while reducing nesting.
• needless_borrow
  Removed superfluous references so functions receive owned or already-borrowed values directly.
• modulo_one
  Avoided computing a remainder by 1. Instead, added explicit branches (e.g., return a constant true vector when density is 1).
• wrong_self_convention
  Renamed methods from into_* to to_* when they take &self, aligning with naming conventions.
• extra-unused-type-parameters
  Dropped unused generic parameters and updated all call sites to match the leaner signatures.
• field-reassign-with-default
  Used struct update syntax (Struct { field, ..Default::default() }) to set fields during construction rather than mutating after a Default init.
• ptr_arg
  Switched function parameters from &Vec<> to the more general &[], avoiding unnecessary allocations.
• cast_lossless
  Replaced as f64 casts with f64::from(...) to prevent potential silent loss and satisfy lint expectations.
• default_trait_access
  Called typed ::default() constructors (e.g., BTreeMap::default()) instead of Default::default() for clarity.