CoPilot comment: Fix dangling `string_view` in `TreeRegexp` copy constructor/assignment

GroupBuilder stores a std::string_view pattern that references the originating TreeRegexp::storedPattern. The current copy constructor and copy-assignment operator shallow-copy rootGroupBuilder, which means the new object's group builder tree still points into other.storedPattern rather than into this->storedPattern.

If other is destroyed (or its storedPattern is moved/mutated via copy-assignment) before the copy is used, the string_views dangle.

Fix: Rebuild the group tree from the freshly stored pattern in both the copy constructor and copy-assignment operator:

TreeRegexp::TreeRegexp(const TreeRegexp& other)
    : storedPattern{ other.storedPattern }
    , regexStrategy{ CreateRegexStrategy(storedPattern) }
    , rootGroupBuilder{ CreateGroupBuilder(storedPattern) }  // rebuild from this->storedPattern
{}

TreeRegexp& TreeRegexp::operator=(const TreeRegexp& other)
{
    storedPattern = other.storedPattern;
    regexStrategy = CreateRegexStrategy(storedPattern);
    rootGroupBuilder = CreateGroupBuilder(storedPattern);  // rebuild from this->storedPattern
    return *this;
}

This mirrors what the primary constructor does and ensures all string_views point into this->storedPattern.

File: cucumber_cpp/library/cucumber_expression/TreeRegexp.cpp (lines ~191–207)

Start in cucumber_cpp/library/cucumber_expression/TreeRegexp.cpp around lines 191–207 and compare the copy constructor and assignment operator with the primary constructor. Confirm that both rebuild the group tree from the copied object's stored pattern, then verify copied and assigned TreeRegexp instances remain valid after the source is destroyed or changed.