feat(rpc): Allow negative heights in rpc methods #2644

Job	Run time
Check Cargo.lock is up to date	8m 19s
Check deny.toml bans	46s
Install zebrad from lockfile without cache on ubuntu-latest	8m 44s
Check deny.toml bans --features default-release-binaries	45s
Test stable on ubuntu-latest	41m 46s
Check deny.toml bans --all-features	46s
Test beta on ubuntu-latest	42m 17s
Check deny.toml sources	49s
Check for unused dependencies	58s
Check deny.toml sources --features default-release-binaries	48s
Test stable on macos-latest	47m 38s
Test stable on windows-latest	1h 4m 22s
Check deny.toml sources --all-features	44s
Test beta on windows-latest	1h 6m 11s
Open or update issues for OS integration failures	0s
	4h 44m 53s

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