Add temporal semantics

[frlai]

Summary

Adds graph-level and temporal semantic metadata support to LEAPP YAML export.

Changes

• Added GraphConfigs for graph-level metadata passed through leapp.compile_graph(...).
• Emits graph-level config fields under pipeline.configs, e.g. frequency and flattened extra values.
• Added TemporalPeriodMs for marking a tensor axis as temporal through TensorSemantics.element_names.
• Serializes temporal axes with the reserved __temporal_axis__ sentinel and temporal_period_ms.
• Exported GraphConfigs and TemporalPeriodMs from the public leapp package.
• Updated semantic metadata docs and API docs with graph-level semantics and temporal-axis examples.
• Added functional coverage for GraphConfigs and TemporalPeriodMs YAML output.

Example

leapp.compile_graph(
    graph_configs=GraphConfigs(
        frequency=50,
        extra={"runtime": "isaac_lab"},
    ),
)

TensorSemantics(
    name="actions",
    ref=actions,
    element_names=[TemporalPeriodMs(100), ["hip", "knee", "ankle"]],
)

Final yaml:

...

outputs:
- name: actions
  element_names:
  - [__temporal_axis__, [hip, knee, ankle]]
  temporal_period_ms: 100
  
pipeline:
  configs:
    frequency: 50
    runtime: isaac_lab
 ...