Handle full contraction in Flops computation

[ajay-mk]

• Update Flops::operator() to handle the case where tensor × tensor → scalar
• Test with CC energy-like expression

[Copilot]

Pull request overview

Updates flop-cost computation to correctly account for tensor–tensor products that fully contract to a scalar (e.g., CC energy expressions), and adds a regression test covering this case.

Changes:

• Extend Flops::operator() to handle tensor × tensor → scalar products.
• Add a unit test for a CC energy-like scalar expression and its expected asymptotic cost.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
SeQuant/core/eval/eval_node.hpp	Adds a scalar-result path for tensor–tensor products in flop-cost estimation.
tests/unit/test_eval_node.cpp	Adds a regression test validating scalar-result contractions and expected asy_cost.

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[bimalgaudel]

This code:

• has not been updated in long time
• only assumes occupied and virtuals (unoccupied) orbital spaces
• maybe should be deprecated..

[evaleev]

This code:

• has not been updated in long time
• only assumes occupied and virtuals (unoccupied) orbital spaces
• maybe should be deprecated..

@bimalgaudel Will the revisions in #462 make this obsolete?

[bimalgaudel]

This code:

• has not been updated in long time
• only assumes occupied and virtuals (unoccupied) orbital spaces
• maybe should be deprecated..

@bimalgaudel Will the revisions in #462 make this obsolete?

AsyCost will not be directly addressed, however, we will have a better (more efficient) mechanism to represent the symbolic cost in terms of all indices present rather than occ or virt. AsyCost class right now does not do much. So I suggest we drop it.

[ajay-mk]

@evaleev @bimalgaudel Can I merge this now? We can deprecate or remove AsyCost in #462.