fix: remove duplicate span exports causing double traces

[AAgnihotry]

Summary

Removes redundant span exporting from StudioWebProgressReporter that was causing duplicate traces in evaluations.

Changes

• Removed spans_exporter parameter and all manual span exporting logic from StudioWebProgressReporter
• Removed deprecated methods: _send_parent_trace(), _send_eval_run_trace(), _send_evaluator_traces()
• Updated tests to reflect the removal of mock_exporter

Why

All span exporting is now handled exclusively by LiveTrackingSpanProcessor in _runtime.py, which was introduced to provide real-time span tracking. The manual span exporting in _progress_reporter was redundant and causing duplicate traces.

Testing

• All existing tests pass (1753 passed)
• Verified LiveTrackingSpanProcessor handles all eval-related spans automatically

Development Package

• Use uipath pack --nolock to get the latest dev build from this PR (requires version range).
• Add this package as a dependency in your pyproject.toml:

[project]
dependencies = [
  # Exact version:
  "uipath==2.5.4.dev1011293930",

  # Any version from PR
  "uipath>=2.5.4.dev1011290000,<2.5.4.dev1011300000"
]

[[tool.uv.index]]
name = "testpypi"
url = "https://test.pypi.org/simple/"
publish-url = "https://test.pypi.org/legacy/"
explicit = true

[tool.uv.sources]
uipath = { index = "testpypi" }

[tool.uv]
override-dependencies = [
    "uipath>=2.5.4.dev1011290000,<2.5.4.dev1011300000",
]