go.mod: use tool directive for buf

[thaJeztah]

use a tool directive to define the buf and protoc-gen-go-ttrpc
tools, but use a separate module and go.work to keep the indirect
dependencies out of the module's dependency tree.

go tool still is able to discover the tools because the go.work
merges the nested module.

[thaJeztah]

Nice; it works!

make check-protos
  shell: /usr/bin/bash -e {0}
  env:
    GOTOOLCHAIN: local
🇩 protos
go -C example tool buf generate
go: downloading github.com/bufbuild/buf v1.69.0
go: downloading connectrpc.com/connect v1.19.2
go: downloading buf.build/go/app v0.2.1-0.20260407195847-833f8f978cda
go: downloading github.com/spf13/cobra v1.10.2
go: downloading buf.build/go/interrupt v1.1.0
go: downloading github.com/spf13/pflag v1.0.10
go: downloading gopkg.in/yaml.v3 v3.0.1
go: downloading buf.build/go/standard v0.1.1-0.20260325175353-2b287e071df5
go: downloading google.golang.org/protobuf v1.36.11
go: downloading github.com/google/go-containerregistry v0.21.5
go: downloading buf.build/gen/go/bufbuild/registry/protocolbuffers/go v1.36.11-20260126144947-819582968857.1
go: downloading buf.build/go/bufplugin v0.10.0
go: downloading github.com/google/uuid v1.6.0
go: downloading github.com/quic-go/quic-go v0.59.0
go: downloading github.com/bufbuild/protocompile v0.14.2-0.20260429155904-12ef1ef2ce91
go: downloading go.lsp.dev/jsonrpc2 v0.10.0
go: downloading github.com/cli/browser v1.3.0
go: downloading buf.build/go/bufprivateusage v0.1.0
go: downloading buf.build/go/protovalidate v1.2.0
go: downloading buf.build/go/protoyaml v0.6.0
go: downloading connectrpc.com/otelconnect v0.9.0
go: downloading github.com/bufbuild/protoplugin v0.0.0-20260414125817-25d1d281b46b
go: downloading golang.org/x/term v0.42.0
go: downloading github.com/mattn/go-colorable v0.1.14
go: downloading github.com/cpuguy83/go-md2man/v2 v2.0.7
go: downloading go.yaml.in/yaml/v3 v3.0.4
go: downloading buf.build/gen/go/bufbuild/protodescriptor/protocolbuffers/go v1.36.11-20250109164928-1da0de137947.1
go: downloading pluginrpc.com/pluginrpc v0.5.0
go: downloading golang.org/x/mod v0.35.0
go: downloading buf.build/go/spdx v0.2.0
go: downloading github.com/moby/moby/api v1.54.2
go: downloading github.com/moby/moby/client v0.4.1
go: downloading github.com/jdx/go-netrc v1.0.0
go: downloading github.com/klauspost/compress v1.18.5
go: downloading github.com/docker/cli v29.4.1+incompatible
go: downloading github.com/mitchellh/go-homedir v1.1.0
go: downloading golang.org/x/sync v0.20.0
go: downloading github.com/opencontainers/go-digest v1.0.0
go: downloading github.com/rs/cors v1.11.1
go: downloading buf.build/gen/go/bufbuild/bufplugin/protocolbuffers/go v1.36.11-20250718181942-e35f9b667443.1
go: downloading buf.build/gen/go/bufbuild/registry/connectrpc/go v1.19.2-20260126144947-819582968857.1
go: downloading github.com/tetratelabs/wazero v1.11.0
go: downloading buf.build/gen/go/bufbuild/protovalidate/protocolbuffers/go v1.36.11-20260415201107-50325440f8f2.1
go: downloading github.com/google/cel-go v0.28.0
go: downloading go.lsp.dev/protocol v0.12.0
go: downloading go.lsp.dev/uri v0.3.0
go: downloading go.uber.org/zap v1.27.1
go: downloading mvdan.cc/xurls/v2 v2.6.0
go: downloading github.com/segmentio/encoding v0.5.4
go: downloading golang.org/x/net v0.53.0
go: downloading golang.org/x/sys v0.46.0
go: downloading github.com/quic-go/qpack v0.6.0
go: downloading go.opentelemetry.io/otel v1.43.0
go: downloading go.opentelemetry.io/otel/metric v1.43.0
go: downloading go.opentelemetry.io/otel/trace v1.43.0
go: downloading github.com/gofrs/flock v0.13.0
go: downloading github.com/mattn/go-isatty v0.0.22
go: downloading github.com/russross/blackfriday/v2 v2.1.0
go: downloading github.com/klauspost/pgzip v1.2.6
go: downloading buf.build/gen/go/pluginrpc/pluginrpc/protocolbuffers/go v1.36.11-20241007202033-cf42259fcbfc.1
go: downloading github.com/containerd/errdefs v1.0.0
go: downloading github.com/containerd/errdefs/pkg v0.3.0
go: downloading github.com/distribution/reference v0.6.0
go: downloading github.com/russross/blackfriday v1.6.0
go: downloading github.com/docker/go-connections v0.7.0
go: downloading github.com/opencontainers/image-spec v1.1.1
go: downloading go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.68.0
go: downloading github.com/sirupsen/logrus v1.9.4
go: downloading cel.dev/expr v0.25.1
go: downloading google.golang.org/genproto/googleapis/api v0.0.0-20260427160629-7cedc36a6bc4
go: downloading go.lsp.dev/pkg v0.0.0-20210717090340-384b27a52fb2
go: downloading go.uber.org/multierr v1.11.0
go: downloading github.com/segmentio/asm v1.2.1
go: downloading golang.org/x/crypto v0.50.0
go: downloading golang.org/x/text v0.36.0
go: downloading github.com/go-logr/logr v1.4.3
go: downloading github.com/tidwall/btree v1.8.1
go: downloading golang.org/x/exp v0.0.0-20260410095643-746e56fc9e2f
go: downloading github.com/rivo/uniseg v0.4.7
go: downloading github.com/docker/go-units v0.5.0
go: downloading github.com/moby/docker-image-spec v1.3.1
go: downloading github.com/docker/docker-credential-helpers v0.9.6
go: downloading github.com/felixge/httpsnoop v1.0.4
go: downloading github.com/containerd/stargz-snapshotter/estargz v0.18.2
go: downloading github.com/antlr4-go/antlr/v4 v4.13.1
go: downloading google.golang.org/genproto/googleapis/rpc v0.0.0-20260427160629-7cedc36a6bc4
go: downloading github.com/go-logr/stdr v1.2.2
go: downloading go.opentelemetry.io/auto/sdk v1.2.1
go: downloading github.com/cespare/xxhash/v2 v2.3.0
go: downloading github.com/vbatts/tar-split v0.12.3
go tool buf generate