Merge branch 'ps/reftable-sign-compare'

The reftable/ library code has been made -Wsign-compare clean.

* ps/reftable-sign-compare:
  reftable: address trivial -Wsign-compare warnings
  reftable/blocksource: adjust `read_block()` to return `ssize_t`
  reftable/blocksource: adjust type of the block length
  reftable/block: adjust type of the restart length
  reftable/block: adapt header and footer size to return a `size_t`
  reftable/basics: adjust `hash_size()` to return `uint32_t`
  reftable/basics: adjust `common_prefix_size()` to return `size_t`
  reftable/record: handle overflows when decoding varints
  reftable/record: drop unused `print` function pointer
  meson: stop disabling -Wsign-compare

meson.build

@@ -708,7 +708,6 @@ if get_option('warning_level') in ['2','3', 'everything'] and compiler.get_argum
     # These are disabled because we have these all over the place.
     '-Wno-empty-body',
     '-Wno-missing-field-initializers',
-    '-Wno-sign-compare',
   ]
     if compiler.has_argument(cflag)
       libgit_c_args += cflag