fix: empty slice panics in bead_sort, bogo_sort, comb_sort and wave_sort

[SEPURI-SAI-KRISHNA]

Pull Request Template

Description

Four algorithms in src/sorting/ panic when handed an empty slice. Sorting nothing should
be a no-op, and the other 30 sorts in the module already treat it that way — 20 of them have
an explicit empty() test. These four were simply never exercised on that input.

sorting::bead_sort(&mut []);                 // index out of bounds: the len is 0 but the index is 0
sorting::bogo_sort(&mut [] as &mut [i32]);   // attempt to subtract with overflow
sorting::comb_sort(&mut [] as &mut [i32]);   // attempt to subtract with overflow
sorting::wave_sort(&mut [] as &mut [i32]);   // attempt to subtract with overflow

Each is an unsigned underflow or an unchecked first-element read:

• bead_sort — let mut max = a[0]; reads element 0 before checking the slice is
  non-empty. Now returns early; there is no bead grid to build.
• bogo_sort — the private is_sorted helper loops for i in 0..len - 1, which
  underflows to usize::MAX at len == 0. Rewritten with windows(2), which naturally
  yields nothing below two elements. This also drops a hand-rolled loop in favour of the
  same idiom sorting::is_sorted already uses.
• comb_sort — gap is clamped to a minimum of 1, so for i in 0..arr.len() - gap
  underflows at arr.len() == 0. Now returns early for fewer than two elements.
• wave_sort — for i in (0..n - 1).step_by(2) underflows at n == 0. Now uses
  n.saturating_sub(1).

These are release-mode hazards as well as debug-mode panics: with overflow checks off, the
underflowed bound becomes a near-usize::MAX loop bound and the sort runs off the end of
the slice.

Tests

empty and one_element cases added to all four, following the module's existing
convention of asserting with the shared is_sorted / have_same_elements helpers.
bead_sort also gains an all_zeroes case, since a maximum of 0 is the other way its
bead grid can end up with zero columns. All new tests run in well under 300ms.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• I ran bellow commands using the latest version of rust nightly.
• I ran cargo clippy --all -- -D warnings just before my last commit and fixed any issue that was found.
• I ran cargo fmt just before my last commit.
• I ran cargo test just before my last commit and all tests passed.
• I added my algorithm to the corresponding mod.rs file within its own folder, and in any parent folder(s).
• I added my algorithm to DIRECTORY.md with the correct link.
• I checked COUNTRIBUTING.md and my code follows its guidelines.

Note: no mod.rs or DIRECTORY.md change was needed — this fixes existing entries rather
than adding a new algorithm.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.90%. Comparing base (2c53ddf) to head (0f1909e).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1063      +/-   ##
==========================================
+ Coverage   95.89%   95.90%   +0.01%     
==========================================
  Files         396      396              
  Lines       30440    30492      +52     
==========================================
+ Hits        29190    29243      +53     
+ Misses       1250     1249       -1     

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