fix: populate dolt_statistics created_at

[CBOSSX]

Summary

• Fixes: After ANALYZE TABLE creates fresh statistics, every dolt_statistics.created_at value is 0001-01-01 00:00:00 instead of the collection time.
• Root cause: StatsController creates both table-scan and index Statistic values without setting their Created field, so the presentation layer receives Go's zero time even though the controller already has a mockable collection clock.

Closes #10168.

Regression evidence

• Before: CGO_CPPFLAGS=-I/opt/homebrew/opt/icu4c/include CGO_LDFLAGS=-L/opt/homebrew/opt/icu4c/lib go test ./libraries/doltcore/sqle/statspro -run '^TestStatisticCreatedAt$' -count=1 -v exited 1

• After: CGO_CPPFLAGS=-I/opt/homebrew/opt/icu4c/include CGO_LDFLAGS=-L/opt/homebrew/opt/icu4c/lib go test ./libraries/doltcore/sqle/statspro -run '^TestStatisticCreatedAt$' -count=1 -v exited 0

Verification

• CGO_CPPFLAGS=-I/opt/homebrew/opt/icu4c/include CGO_LDFLAGS=-L/opt/homebrew/opt/icu4c/lib go test -vet=off -timeout 45m ./libraries/doltcore/sqle/statspro -count=1
• CGO_CPPFLAGS=-I/opt/homebrew/opt/icu4c/include CGO_LDFLAGS=-L/opt/homebrew/opt/icu4c/lib GOFLAGS=-mod=readonly go build ./...
• CGO_CPPFLAGS=-I/opt/homebrew/opt/icu4c/include CGO_LDFLAGS=-L/opt/homebrew/opt/icu4c/lib go vet -mod=readonly ./...
• go run -mod=readonly ./utils/copyrightshdrs/; ./Godeps/verify.sh; ./utils/repofmt/check_bats_fmt.sh; ./utils/repofmt/check_fmt.sh

Scope

• 2 files changed, +28 / -0 lines