Fix false "failed to find library" warning for use clauses of generic packages

[tasgomes]

Problem

When a design unit brings a locally declared generic package (or a local package instantiation) into scope with a use clause, the VHDL dependency scanner mistakes the package name for a library name and emits a spurious warning.

Example (VHDL-2008 generic package interface):

entity my_th is
    generic(
        package th_pkg is new work.some_pkg generic map (<>)
    );
end entity;

architecture a of my_th is
    use th_pkg.all;   -- th_pkg is a formal generic package, not a library
begin
end architecture;

This produces:

WARNING - /(...)/my_th.vhd: failed to find library 'th_pkg'

th_pkg is a formal generic-package parameter visible by its simple name, not a library. Compilation and simulation succeed, so only the (misleading) warning is wrong.

Root cause

VHDLReference._find_uses() parses use th_pkg.all; and records a package reference with library="th_pkg". The parser already recognizes the package th_pkg is new work.some_pkg ... instantiation (via PACKAGE_INSTANCE_PATTERN), but it never uses that knowledge to suppress the bogus library reference, so Project later fails to resolve library th_pkg and warns.

Fix

In VHDLReference.find(), collect the names introduced by local/generic package instantiations (the new_name group of PACKAGE_INSTANCE_PATTERN) and drop any package reference whose library matches one of them.

The real dependency (the reference to the instantiated package, e.g. work.some_pkg) has library="work" and is preserved, so the dependency graph is unchanged.

Tests

Added test_use_of_local_package_instance_is_not_a_library_reference in tests/unit/test_vhdl_parser.py, covering both a generic package formal and a local package instance, each followed by a use ...all; clause. It asserts that only the real package references remain. The test fails on main and passes with this change; the full parser suite still passes.

Notes

Fixes a false positive only; the dependency graph and compile order are unaffected.