[LGR] Support writing NNA blocks for cross-LGR NNC connections

[arturcastiel]

Support writing NNA blocks for cross-LGR NNC connections

Description

This PR extends the EGRID writer to support cross-LGR NNC connections using the NNA keywords.
Previously, only the following NNC types were written:

• Same-grid NNC (NNC1 / NNC2)
• Local–global NNC (NNCL / NNCG)

Connections between two different LGR grids were not written to the EGRID file.
This PR adds support for those connections via:

• NNCHEADA
• NNA1
• NNA2

Implementation

The following changes were introduced:

• Added save_nna() to write cross-grid NNC blocks.
• Iteration over NNCCollection::diff_grid_nnc() to detect connections between different grids.
• Skip global-grid connections (grid = 0) in the NNA stage since those are written as NNCL/NNCG.
• Simplified save_nnc_local_global() by removing the local_first parameter and assuming the normalized ordering provided by NNCDiffGrid.

New output structure:

Connection type	Keywords written
Same grid	NNCHEAD, NNC1, NNC2
LGR–Global	NNCHEAD, NNCL, NNCG
LGR–LGR	NNCHEADA, NNA1, NNA2

Tests

Added a new integration test:

tests/parser/integration/NNCTestsLGR.cpp

The test:

• Constructs an NNCCollection containing:
  • global NNCs
  • same-grid LGR NNCs
  • LGR–global cross-grid NNCs
  • LGR–LGR cross-grid NNCs
• Verifies that the correct blocks are produced and that the indices match expectations.

Bug fixes

save_nnc_local_global was also simplified, ensuring consistent order of NNCL and NNCG. Tests were changed accordingly.

[arturcastiel]

jenkins build this please

[arturcastiel]

jenkins build this please

[bska]

Very good. I'll merge into master.