feat: Relax GrpcMethod lifetime #2483

Job	Run time
codegen	27s
cargo-deny check	24s
Check MSRV	1m 2s
Interop Tests (ubuntu-latest)	38s
rustfmt	10s
test (ubuntu-latest)	2m 45s
Interop Tests (macOS-latest)	46s
test (macOS-latest)	1m 41s
Check unused dependencies (ubuntu-latest)	3m 38s
Interop Tests (windows-latest)	3m 4s
test (windows-latest)	5m 4s
Check unused dependencies (macOS-latest)	4m 16s
check (ubuntu-latest)	1m 20s
Check unused dependencies (windows-latest)	6m 51s
check (macOS-latest)	1m 11s
check (windows-latest)	3m 0s
	36m 17s

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