The previous instrumentation filter ('^//src,^//include,-^//src/farmhash')
failed to match the root library target ('//:zetasketch-cpp') due to
wildcard expansion rules in Bazel when matching labels. This caused the
root library to remain un-instrumented in CI.
Because no targets were instrumented, the coverage test actions matched
the standard 'bazel test' action keys, hitting the test cache. Standard
test execution does not produce 'coverage.dat' artifacts, resulting in
LcovMerger failing with 'There was no coverage found'.
This commit replaces the filter with '^//[^/]*:.*$' (identical to the
rowkeydb repository configuration). This correctly matches all top-level
targets (including the root library) while implicitly excluding
sub-packages (such as '//src/farmhash:farmhash'). This ensures
coverage profiling is correctly generated for the root library without
requiring the '--nocache_test_results' workaround.