[SYSTEMDS-3953] Switch quantile default to R quantile type 7

[MegaByteTron]

Summary

Fixes both issues reported in SYSTEMDS-3953:
scalar p vs matrix p returning different answers because the
average flag was not propagated from pickValues to pickValue, and
even-n inputs averaging the two order statistics straddling ceil(p·n)
— which matches R type 7 only at p = 0.5 and matches nothing named in
Hyndman & Fan (1996) elsewhere.

Switches the SystemDS default to R quantile type 7 across the kernel,
CP, SP, and FED paths. Supersedes PR #2497
([SYSTEMDS-3922]/[SYSTEMDS-3898]) which patched averaging on even n only
for p = 0.5. Continues PR #2565
by @ywcb00 which added the failing-tests-as-@Ignore scaffolding
(d6aabf6867); those tests are un-ignored here.

IQM is intentionally preserved — it is a trimmed weighted mean, not an
order-statistic pick, and does not fit the type-7 interpolation shape.
IQMTest is the guardrail.

R type 7 (1-indexed, n = |x|):

h  = (n − 1) · p + 1
lo = floor(h)                 // clamped to [1, n]
hi = min(lo + 1, n)
g  = h − lo                   // in [0, 1)
Q  = (1 − g) · x[lo] + g · x[hi]

Ticket example — [0.239, 0.517, 0.890, 0.944] at p = 0.25, 0.5, 0.75
now returns 0.4475, 0.7035, 0.9035, matching R.

Commit 1 — [SYSTEMDS-3953] Switch quantile kernel to R quantile type 7

MatrixBlock.computeType7Rank(long n, double p) is the new static
helper returning {lo, hi, g} — one primitive every consumer picks
against so the formula lives in one place. pickUnweightedValue /
pickWeightedValue / pickValues / median rewired to type 7;
pickValue(double) becomes the public API and the pickValue(double, boolean average) overload is deleted. QuantilePickCPInstruction
drops the matBlock.getLength() % 2 == 0 argument. QuantilePickTest
expected values updated to type 7; CompressedSortTest drops the
now-dead pickValue(q, true) averaging assertion.

Commit 2 — [SYSTEMDS-3953] Rework Spark quantile pick to R type 7

processInstruction becomes a clean switch: VALUEPICK / MEDIAN →
pickQuantileValues, IQM → new private computeIqm. The pre-3953
shape mixed both under a getWeightedQuantileSummary blob whose fields
meant different things per operation. pickQuantileValues handles
N ≥ 1 quantiles uniformly; weighted branch pulls (lo, hi, g) triples
from a new shared extractWeightedTriples helper. Type7Rank inner
class and getWeightedQuantileSummary removed.

Un-ignore testQuartileArray{CP,SP} (marked FIXME: fix SYSTEMDS-3953
by David in d6aabf6867) and add testQuantileEven{1,2,3}{CP,SP} at
n = 128 — the odd-length default (n = 1973) can't exercise g ≠ 0
interpolation because at classical p the rank lands on an integer.

Commit 3 — [SYSTEMDS-3953] Switch federated quantile pick to R type 7

processRowQPick computes per-quantile rank triples (lo, hi, g) up
front, flattens to a deduplicated int[] of ranks, feeds those to
pickMultipleRanks (renamed from computeMultipleQuantiles to signal
its narrowed job), and interpolates at the caller. Decoupling ranks
from interpolation keeps the multi-rank pipeline type-7-agnostic.
Consequence: the boolean average thread across four signatures
(processRowQPick, createHistogram, getBucketWithIndex,
getSingleQuantileResult) is removed end-to-end. computeIqm mirrors
the SP helper from commit 2 so the two paths read symmetrically.
refineBucket shares the coarse-histogram refinement heuristic between
computeIqm and pickMultipleRanks. MEDIAN in processColumnQPick
dispatches through VALUEPICK with p = 0.5; the ColMedian inner UDF
goes away.

Weighted row-federated inherits the kernel's sum-of-weights extension
(N = Σw) for free. Column-federated weighted stays out of scope,
matching PR #2497.