fix: routinegroup & etcd watch goroutine leak

[Nanosk07]

fix a goroutine leak issue that occurs when a gRPC call is made after the connection transitions to the idle state. The issue persists under similar circumstances as described in #4490.

I tested #4490 locally, it just cleaned the listener and did not resolve the leak. Therefore, I referred to the original commit code and added additional code to address the issue.

[codecov]

Codecov Report

Attention: Patch coverage is 58.06452% with 26 lines in your changes missing coverage. Please review.

Project coverage is 94.44%. Comparing base (8690859) to head (6c5332a).
Report is 189 commits behind head on master.

Files with missing lines	Patch %	Lines
core/discov/internal/registry.go	56.36%	23 Missing and 1 partial ⚠️
core/discov/subscriber.go	66.66%	1 Missing ⚠️
zrpc/resolver/internal/discovbuilder.go	0.00%	1 Missing ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
zrpc/resolver/internal/resolver.go	100.00% <100.00%> (ø)
core/discov/subscriber.go	81.51% <66.66%> (-3.31%)	⬇️
zrpc/resolver/internal/discovbuilder.go	37.03% <0.00%> (-1.43%)	⬇️
core/discov/internal/registry.go	76.26% <56.36%> (-2.65%)	⬇️

... and 4 files with indirect coverage changes