Fix PSAR series assignment to use .iloc consistently

[saket3395]

Summary

Fixes #354, #357, #339, #348 — all four report the same root cause independently.

In PSARIndicator._run (ta/trend.py), one line uses bare positional indexing:

if high2 > self._psar.iloc[i]:
    self._psar[i] = high2          # inconsistent / deprecated
elif high1 > self._psar.iloc[i]:
    self._psar.iloc[i] = high1     # already correct

Every other read/write of self._psar in this method already goes through .iloc[i]. The one exception triggers pandas' FutureWarning: Series.__setitem__ treating keys as positions is deprecated (reported in #357, #339, #348) and was also flagged directly as an indexing inconsistency in #354, which includes the exact proposed fix.

Change

self._psar[i] = high2

→

self._psar.iloc[i] = high2

One line, no behavior change — .iloc[i] and positional [i] currently resolve to the same element for this integer-indexed Series; the fix only removes the deprecated code path and makes the method internally consistent.

Test plan

• Confirmed via source inspection that this is the only remaining bare-positional assignment on self._psar in the method — all other accesses already use .iloc.
• Change matches the fix proposed in Bug Report - Incorrect Series Indexing in trend.py (Line 1030) #354 exactly.
• Not run through the project's test suite locally — flagging for maintainer/CI verification.