der: optimize compile-time: code reuse with encode_value_to_slice

[dishmaker]

before:

formats$ cargo llvm-lines -p der --all-features --release | head -n 8
  Lines                Copies             Function name
  -----                ------             -------------
  53357                920                (TOTAL)
   6352 (11.9%, 11.9%)  29 (3.2%,  3.2%)  der::asn1::any::AnyRef::decode_as_encoding
   2330 (4.4%, 16.3%)   10 (1.1%,  4.2%)  der::asn1::integer::value_cmp
    915 (1.7%, 18.0%)    5 (0.5%,  4.8%)  der::asn1::integer::int::decode_to_array
    904 (1.7%, 19.7%)   16 (1.7%,  6.5%)  std::thread::local::LocalKey<T>::try_with
    872 (1.6%, 21.3%)    1 (0.1%,  6.6%)  <der::error::ErrorKind as core::fmt::Display>::fmt

after:

formats$ cargo llvm-lines -p der --all-features --release | head -n 8
  Lines                Copies             Function name
  -----                ------             -------------
  52897                930                (TOTAL)
   6352 (12.0%, 12.0%)  29 (3.1%,  3.1%)  der::asn1::any::AnyRef::decode_as_encoding
   1350 (2.6%, 14.6%)   10 (1.1%,  4.2%)  der::asn1::integer::value_cmp
    915 (1.7%, 16.3%)    5 (0.5%,  4.7%)  der::asn1::integer::int::decode_to_array
    904 (1.7%, 18.0%)   16 (1.7%,  6.5%)  std::thread::local::LocalKey<T>::try_with
    872 (1.6%, 19.6%)    1 (0.1%,  6.6%)  <der::error::ErrorKind as core::fmt::Display>::fmt

[tarcieri]

Since this is just a helper function for / implementation detail of value_cmp, can you nest it inside there?

[dishmaker]

It's useful in few other places.

[dishmaker]

Optimized from 53357 to 52248 lines

$ cargo llvm-lines -p der --all-features --release | head -n 8
  Lines                Copies             Function name
  -----                ------             -------------
  52248                930                (TOTAL)
   6352 (12.2%, 12.2%)  29 (3.1%,  3.1%)  der::asn1::any::AnyRef::decode_as_encoding
   1350 (2.6%, 14.7%)   10 (1.1%,  4.2%)  der::asn1::integer::value_cmp
    915 (1.8%, 16.5%)    5 (0.5%,  4.7%)  der::asn1::integer::int::decode_to_array
    904 (1.7%, 18.2%)   16 (1.7%,  6.5%)  std::thread::local::LocalKey<T>::try_with
    872 (1.7%, 19.9%)    1 (0.1%,  6.6%)  <der::error::ErrorKind as core::fmt::Display>::fmt