Support tile removal via existence field in architecture spec

[YanzhouTang]

Added support for existence: false in tile_overrides to remove tiles from the architecture.

Modified link creation logic to skip removed tiles, preventing crashes when building mesh topology.

[tancheng]

Can we have a FIR test inside https://github.com/coredac/dataflow/tree/main/test, make it consume a custom_arch.yaml

dataflow/test/e2e/fir/fir_kernel.mlir

Line 17 in 75b6fbc

// RUN: --architecture-spec=../../arch_spec/architecture.yaml \

And verify the after mapping IR has no operation mapped onto the tile that is removed.

[YanzhouTang]

Can we have a FIR test inside https://github.com/coredac/dataflow/tree/main/test, make it consume a custom_arch.yaml

dataflow/test/e2e/fir/fir_kernel.mlir

Line 17 in 75b6fbc

// RUN: --architecture-spec=../../arch_spec/architecture.yaml \

And verify the after mapping IR has no operation mapped onto the tile that is removed.

I've added a testcase based on fir kernel, removing tile (0,1) and tile (1,1) which are used in normal fir kernel.