Implement -noleaf

[hanbings]

We use the walkdir library for directory traversal in our codebase, and the current predicates are all secondary filtering on the results returned by walkdir. So I guess -noleaf will not bring any optimization (unless walkdir includes this optimization, to be honest I don't know much about walkdir and didn't find any related functions in their documentation).

The current code only contains compatibility code.

Closes #376

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 65.58%. Comparing base (3bf5567) to head (e9fcdaf).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #414      +/-   ##
==========================================
+ Coverage   65.55%   65.58%   +0.03%     
==========================================
  Files          34       34              
  Lines        3942     3952      +10     
  Branches      902      904       +2     
==========================================
+ Hits         2584     2592       +8     
  Misses       1002     1002              
- Partials      356      358       +2     

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[github-actions]

Commit 38322c0 has GNU testsuite comparison:

Run GNU findutils tests: GNU tests summary = TOTAL: 702 / PASS: 445 / FAIL: 254 / ERROR: 2
Run GNU findutils tests: Changes from main: PASS +0 / FAIL +0 / ERROR +0 / SKIP +0 
Run GNU findutils tests: Gnu tests No changes
Run BFS tests: Changes from main: PASS +1 / SKIP +0 / FAIL -1
Run BFS tests: BFS tests summary = TOTAL: 288 / PASS: 191 / SKIP: 1 / FAIL: 96

[sylvestre]

LGTM
Maybe we should create a doc like compatibility.md to keep track of these flags that aren't doing anything but here for compat. WDYT ?

[github-actions]

Commit e9fcdaf has GNU testsuite comparison:

Run GNU findutils tests: GNU tests summary = TOTAL: 702 / PASS: 445 / FAIL: 254 / ERROR: 2
Run GNU findutils tests: Changes from main: PASS +0 / FAIL +0 / ERROR +0 / SKIP +0 
Run GNU findutils tests: Gnu tests No changes
Run BFS tests: Changes from main: PASS +1 / SKIP +0 / FAIL -1
Run BFS tests: BFS tests summary = TOTAL: 288 / PASS: 191 / SKIP: 1 / FAIL: 96

[hanbings]

LGTM Maybe we should create a doc like compatibility.md to keep track of these flags that aren't doing anything but here for compat. WDYT ?

Sound like a perfect idea, we cannot assume that every user will review the code to determine compatibility.
I'll submit them in a new PR later. :)