Adds stream interface for parseLibertyFile

[QuantamHD]

This allows users of the STA api to read liberty from an in memory copy.

[CLAassistant]

All committers have signed the CLA.

[dsengupta0628]

<istream> is fine but <iosfwd> would suffice in LibertyParser.hh since only a reference is declared, slightly reducing transitive include cost across the many translation units that pull in this header

[dsengupta0628]

Please remove blank line here.

[dsengupta0628]

Please add a comment here "// Parse Liberty from an in-memory stream.
// filename is used only as a label in diagnostic messages;
// it need not correspond to a file on disk."

It was a bit confusing to me how file_contents and filename interacted- but once I got it, I think it makes sense to add a one-line explanation.

[dsengupta0628]

It would be nice to have a stream based unit testcase. Here is something you can add as a C++ unit test to liberty/test/cpp/TestLibertyStaCallbacks.cc. It mirrors the existing ParserSaveAll test but exercises the new stream overload, and crucially it uses no temp file, which is the point of the new API.

// Verifies in-memory parsing via std::istream& without touching the filesystem.
  TEST_F(StaLibertyTest, ParserStreamOverload) {
    const char *content = R"(
  library(test_stream_overload) {
    delay_model : table_lookup ;
    time_unit : "1ns" ;
    voltage_unit : "1V" ;
    current_unit : "1mA" ;
    capacitive_load_unit(1, ff) ;
    define(custom_attr, cell, float) ;
    my_variable = 42.0 ;
    cell(SV1) {
      area : 1.0 ;
      pin(A) { direction : input ; capacitance : 0.01 ; }
      pin(Z) { direction : output ; function : "A" ; }
    }
  }
  )";

    // Feed the parser directly from memory — no temp file involved.
    std::stringstream stream(content);
    RecordingLibertyVisitor visitor;
    parseLibertyFile(stream, "<in-memory>", &visitor, sta_->report());

    // Same expectations as the file-path variant: the visitor saw a library
    // group with one define, one variable, and a cell with area=1.0.
    EXPECT_GT(visitor.begin_count, 0);
    EXPECT_EQ(visitor.begin_count, visitor.end_count);
    ASSERT_EQ(visitor.root_groups.size(), 1u);
    const LibertyGroup *library = visitor.root_groups.front();
    ASSERT_NE(library, nullptr);
    EXPECT_EQ(library->defineMap().size(), 1u);
    EXPECT_EQ(visitor.variables.size(), 1u);
    EXPECT_GT(visitor.simple_attrs.size(), 0u);

    const LibertyGroup *cell = library->findSubgroup("cell");
    ASSERT_NE(cell, nullptr);
    float area = 0.0f;
    bool exists = false;
    cell->findAttrFloat("area", area, exists);
    EXPECT_TRUE(exists);
    EXPECT_FLOAT_EQ(area, 1.0f);
  }

You'll also need this include at the top of the file (next to the existing <string>):

#include <sstream>