Add WaveTrend Oscillator indicator

[AlexCatarino]

Description

Implements WaveTrendOscillator (BarIndicator) per issue #6411. Adds the
indicator class, the WTO helper in QCAlgorithm.Indicators.cs, unit tests
inheriting CommonIndicatorTests<IBaseDataBar>, and the TA-Lib-generated
reference CSV under Tests/TestData/spy_wto.txt.

The indicator's Current.Value exposes the main wave trend line (WT1 = EMA of
the channel index). A public Signal property exposes the signal line
(WT2 = SMA of WT1). Formula follows the LazyBear TradingView script:

ESA = EMA(HLC3, n1);  D = EMA(|HLC3 - ESA|, n1)
CI  = (HLC3 - ESA) / (0.015 * D)
WT1 = EMA(CI, n2);    WT2 = SMA(WT1, m)

Default parameters: n1=10, n2=21, m=4.

Related Issue

Closes #6411

Motivation and Context

Community request from the QuantConnect forum (linked in the issue). The
WaveTrend Oscillator is a popular momentum indicator that currently has no
native support in LEAN, forcing users to re-implement it in algorithms.

Requires Documentation Change

Yes — please add the following entry to
Documentation/Resources/indicators/IndicatorImageGenerator.py in the
indicators dict:

'WaveTrend-Oscillator': IndicatorInfo(
    WaveTrendOscillator(10, 21, 4),
    'WaveTrendOscillator(10, 21, 4)',
    'WTO(_symbol, 10, 21, 4)',
    'self.wto(self._symbol, 10, 21, 4)'
),

All parameters are integer periods, so no m suffix is required on the C# entries.

How Has This Been Tested?

• dotnet build QuantConnect.Lean.sln (0 errors)
• dotnet test Tests/ --filter WaveTrendOscillatorTests (13 passed)
• Reference values generated via TA-Lib using the script posted by
  @LouisSzeto in the issue; agreement within 1e-4.

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist:

• My code follows the code style of this project.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.
• My branch follows the naming convention feature-<N>-<description>