feat: expr builder

[seanpearsonuk]

Pull request overview

This PR introduces a new Fluent expression builder subsystem (AST + registry + parser + discovery + builder facade) and integrates it with the solver settings API so expression objects can be assigned directly to setup.named_expressions[...].definition. It also adds a comprehensive set of unit/grammar/discovery/integration tests plus a minimal Fluent smoke test.

Changes:

• Added ansys.fluent.core.expressions package providing an AST, function registry, builder facade, discovery layer, and a recursive-descent parser with round-tripping.
• Extended Textual.set_state() to accept “expression objects” (duck-typed via __fluent_expr__) at whitelisted settings paths.
• Added tests covering parsing, registry coverage, discovery via settings/field-info fakes, flobject integration, and a live Fluent smoke test.

[codacy-production]

Up to standards ✅

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[Copilot]

Pull request overview

This PR introduces a new Fluent expression builder subsystem (AST + registry + parser + discovery + builder facade) and integrates it with the solver settings API so expression objects can be assigned directly to setup.named_expressions[...].definition. It also adds a comprehensive set of unit/grammar/discovery/integration tests plus a minimal Fluent smoke test.

Changes:

• Added ansys.fluent.core.expressions package providing an AST, function registry, builder facade, discovery layer, and a recursive-descent parser with round-tripping.
• Extended Textual.set_state() to accept “expression objects” (duck-typed via __fluent_expr__) at whitelisted settings paths.
• Added tests covering parsing, registry coverage, discovery via settings/field-info fakes, flobject integration, and a live Fluent smoke test.

Reviewed changes

Copilot reviewed 17 out of 17 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
tests/expressions/test_parser.py	Parser unit tests and canonical round-trip coverage.
tests/expressions/test_grammar.py	Grammar coverage tests for reductions/math/vector/conditional APIs.
tests/expressions/test_fluent_smoke.py	Live Fluent smoke test validating end-to-end builder→settings→evaluation.
tests/expressions/test_flobject_expression_integration.py	Offline tests for Textual.set_state expression-object acceptance/rejection by path.
tests/expressions/test_field_info_discovery.py	Tests for discovery behavior using field-info shaped fakes.
tests/expressions/test_expression_builder.py	Core builder/AST/registry behavior tests (rendering, operators, errors).
tests/expressions/test_discovery.py	Tests for settings-tree-driven discovery and slot accessors.
src/ansys/fluent/core/solver/flobject.py	Adds whitelisted-path expression-object support to Textual.set_state().
src/ansys/fluent/core/expressions/errors.py	Introduces ExpressionBuildError.
src/ansys/fluent/core/expressions/builder.py	Implements ExpressionBuilder facade and group/signature invokers.
src/ansys/fluent/core/expressions/_slots.py	Adds per-parameter slot discovery helpers (locations/scalars).
src/ansys/fluent/core/expressions/_registry.py	Declares the function registry, signature/param binding, and Weight enum.
src/ansys/fluent/core/expressions/_parser.py	Implements tokenizer + recursive-descent parser + reverse maps for kind inference.
src/ansys/fluent/core/expressions/_discovery.py	Implements best-effort discovery against settings and/or field-info.
src/ansys/fluent/core/expressions/_ast.py	Adds the typed immutable AST and operator overloading.
src/ansys/fluent/core/expressions/init.py	Public package exports for builder/parser/types.
doc/changelog.d/5252.added.md	Changelog entry for the new expression builder feature.

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