feat: Relax GrpcMethod lifetime #2630

Job	Run time
rustfmt	7s
cargo-deny check	21s
codegen	12s
check (ubuntu-latest)	44s
Interop Tests (ubuntu-latest)	28s
check (macOS-latest)	1m 41s
Check MSRV	27s
Interop Tests (macOS-latest)	30s
check (windows-latest)	2m 44s
test (ubuntu-latest)	2m 47s
Interop Tests (windows-latest)	2m 55s
test (macOS-latest)	1m 19s
Check unused dependencies (ubuntu-latest)	3m 23s
test (windows-latest)	5m 54s
Check unused dependencies (macOS-latest)	2m 49s
Check unused dependencies (windows-latest)	6m 58s
	33m 19s

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