Bug 42156: (QA follow-up) Correct POD typos and demote private helpers

The previous POD follow-up added headings for the private helper subs but
introduced several typos and used =head2, which puts them at the same level
as the public API in the generated docs. This patch:

 - Fixes typos: matchpint, pionts, march matcher, mathcpoints, etc.
 - Clarifies a couple of descriptions.
 - Demotes each private helper from =head2 to =head3 so they render as
   implementation notes rather than peers of the public methods, matching
   the pattern used in Koha::Authority's "Internal methods" block.

Helper subs remain interleaved with the public API in source order to keep
the diff minimal; a wholesale move into a dedicated "Internal functions"
section would be a larger refactor outside the scope of this bug.

Test plan:
 1 - perldoc C4/Matcher.pm
 2 - Confirm no typos are rendered and the private helpers appear one level
     deeper than the public methods.

Signed-off-by: Martin Renvoize <martin.renvoize@openfifth.co.uk>
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>

C4/Matcher.pm

@@ -204,9 +204,9 @@ sub fetch {
     return $self;
 }
 
-=head2 _fetch_matchpoint
+=head3 _fetch_matchpoint
 
-helper function that retrieves a matchpint and components from the DB
+helper function that retrieves a matchpoint and its components from the DB
 
 =cut
 
@@ -277,10 +277,10 @@ sub store {
     return $self->{'id'};
 }
 
-=head2 _del_matcher_components
+=head3 _del_matcher_components
 
-helper function that deletes matchpionts and matchchecks for a matcher
-used to clear existing values before saving new
+helper function that deletes matchpoints and matchchecks for a matcher;
+used to clear existing values before saving new ones
 
 =cut
 
@@ -298,9 +298,9 @@ sub _del_matcher_components {
     # matchpoint_component_norms
 }
 
-=head2 _update_marc_matchers
+=head3 _update_marc_matchers
 
-helper function that updates a march matcher db entry
+helper function that updates a MARC matcher DB entry
 
 =cut
 
@@ -322,9 +322,9 @@ sub _update_marc_matchers {
     );
 }
 
-=head2 _new_marc_matchers
+=head3 _new_marc_matchers
 
-helper function that inserts a new marc matcher entry
+helper function that inserts a new MARC matcher entry
 
 =cut
 
@@ -341,9 +341,9 @@ sub _new_marc_matchers {
     $self->{'id'} = $dbh->{'mysql_insertid'};
 }
 
-=head2 _store_matcher_components
+=head3 _store_matcher_components
 
-helper function that stores the values for mathcpoints and match checks for a matcher
+helper function that stores the values for matchpoints and matchchecks for a matcher
 
 =cut
 
@@ -374,7 +374,7 @@ sub _store_matcher_components {
 
 }
 
-=head2 _store_matchpoint
+=head3 _store_matchpoint
 
 helper function that stores a matchpoint and its components
 
@@ -887,7 +887,7 @@ sub dump {
     return $result;
 }
 
-=head2 _passes_required_checks
+=head3 _passes_required_checks
 
 helper function that checks the match keys for all matched records
 
@@ -907,7 +907,7 @@ sub _passes_required_checks {
     return 1;
 }
 
-=head2 _get_match_keys
+=head3 _get_match_keys
 
 helper function that retrieves the values of the match fields from a source record
 
@@ -1003,7 +1003,7 @@ sub _get_match_keys {
     return @keys;
 }
 
-=head2 _parse_match_component
+=head3 _parse_match_component
 
 helper function to transform a match component into the expected form