feat: hamt: Add public fn clear to reset and clear all entries in HAMT

[snissn]

following up on changes to the KAMT in #2092 this PR changes HAMT to support a clear() method

This PR introduces a new clear method to the Hamt data structure, allowing users to reset the root to an empty node and clear all entries.

Changes:

• Added pub fn clear to Hamt to reset and clear all entries.
• Updated the test suite with test_clear to verify:
  • Entries exist before clearing.
  • Entries are removed after calling clear.
  • The Hamt remains functional post-clear.

This addition enhances usability by providing an efficient way to clear the Hamt.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.95%. Comparing base (e9eef91) to head (7e65b56).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2095      +/-   ##
==========================================
+ Coverage   75.86%   75.95%   +0.09%     
==========================================
  Files         154      154              
  Lines       15743    15778      +35     
==========================================
+ Hits        11943    11984      +41     
+ Misses       3800     3794       -6     

Files with missing lines	Coverage Δ
ipld/hamt/src/hamt.rs	90.99% <100.00%> (+3.49%)	⬆️

... and 1 file with indirect coverage changes

[Stebalien]

Thanks!