Excessive memory usage when generating multiple fakes with `counterfeiter:generate` directives.

[silvestre]

Hi,

generating multiple fakes using multiple counterfeiter:generate directives uses much more memory than when generating them one by one.

Generating 23 fakes with multiple counterfeiter:generate directives:

/bin/time -v go run github.com/maxbrunsfeld/counterfeiter/v6 -generate  
Writing `FakeWSHelper` to `fake_wshelper.go`... Done
[... 22 more fakes ...]
Writing `FakeActiveScheduleSychronizer` to `fake_sychronizer.go`... Done
    Command being timed: "go run github.com/maxbrunsfeld/counterfeiter/v6 -generate"
    User time (seconds): 57.21
    System time (seconds): 19.67
    Percent of CPU this job got: 414%
    Elapsed (wall clock) time (h:mm:ss or m:ss): 0:18.54
[...]
    Maximum resident set size (kbytes): 18870440
[...]
    Exit status: 0

Using multiple //go:generate go run github.com/maxbrunsfeld/counterfeiter/v6 directives:

COUNTERFEITER_NO_GENERATE_WARNING=true /usr/bin/time -v go generate .
Writing `FakeWSHelper` to `fake_wshelper.go`... Done
[... 22 more fakes ...]
Writing `FakeActiveScheduleSychronizer` to `fake_sychronizer.go`... Done
    Command being timed: "go generate ."
    User time (seconds): 121.57
    System time (seconds): 43.26
    Percent of CPU this job got: 365%
    Elapsed (wall clock) time (h:mm:ss or m:ss): 0:45.13
[...]
    Maximum resident set size (kbytes): 1481028
[...]
    Exit status: 0

Using multiple counterfeiter:generate directives cuts down wall clock time by more than half but increases memory usage from 1.4 GiB to 18 GiB.

Maybe there's a memory leak?

$ grep github.com/maxbrunsfeld/counterfeiter/v6 go.mod
    github.com/maxbrunsfeld/counterfeiter/v6 v6.7.0