find: implement {} path substitution for -exec

[Erickkaranja]

A utility_name or argument containing only the two characters "{}" shall be replaced by the current pathname.

[codecov]

Codecov Report

❌ Patch coverage is 33.33333% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.73%. Comparing base (89a5327) to head (a6cd25d).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
src/find/matchers/exec.rs	33.33%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #620      +/-   ##
==========================================
- Coverage   91.76%   91.73%   -0.03%     
==========================================
  Files          31       31              
  Lines        6203     6205       +2     
  Branches      328      329       +1     
==========================================
  Hits         5692     5692              
- Misses        390      391       +1     
- Partials      121      122       +1     

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[RenjiSann]

Suggested change

	let mut command;
	if &self.executable == "{}" {
	command = Command::new(file_info.path());
	} else {
	command = Command::new(&self.executable);
	}
	let mut command =
	if &self.executable == "{}" {
	Command::new(file_info.path())
	} else {
	Command::new(&self.executable)
	};