hplot: make {Horiz,Vert}Line implement DataRanger

Signed-off-by: Sebastien Binet <binet@cern.ch>

all: bump x/deps

Signed-off-by: Sebastien Binet <binet@cern.ch>

groot/riofs: drop mmap-ing ROOT files by default, add file+mmap:// co…

…nvenience protocol

Fixes #1019.

Signed-off-by: Sebastien Binet <binet@cern.ch>

all: bump klauspost/compress@v1.17.9 and x/{crypto,exp,image,text,too…

…ls,mod,net,sys}

Signed-off-by: Sebastien Binet <binet@cern.ch>

hplot: add example for time series

Signed-off-by: Sebastien Binet <binet@cern.ch>

all: bump gioui@v0.30, x/{crypto,exp,image,text,tools}@latest

Signed-off-by: Sebastien Binet <binet@cern.ch>

ci: pin to ubuntu-20.04 for Gio's benefit

With the latest Gio updates, the headless API doesn't seem to render
stable images across machines and OS-stacks.
Pin to Ubuntu-20.04 for the time being.

Signed-off-by: Sebastien Binet <binet@cern.ch>

groot/riofs: provide a stable top-dir to Walk

Signed-off-by: Sebastien Binet <binet@cern.ch>

fmom: update for new gonum.org/v1/gonum@v0.12.0/r3 API

Signed-off-by: Sebastien Binet <binet@cern.ch>

groot/{cmd/root-gen-type,riofs}: add testdata for base+derived classes