fix: better asset canister upload chunking

[viviveevee]

Description

The portal currently cannot sync the new website because it runs into the instruction limit, most likely because of a lot of hashing that happens on the canister side since this is the only significant change between it working and not.

How Has This Been Tested?

Locally tested with a new e2e test that reproduces the issue. Removed again since it takes ~9 minutes to run:

@test "can upload 70 2mb files" {
  install_asset assetscanister
  dfx_start
  assert_command dfx deploy

  # Create 70 files, each 8MB in size
  mkdir -p src/e2e_project_frontend/assets/large_files
  for i in $(seq 1 70); do
    dd if=/dev/urandom of="src/e2e_project_frontend/assets/large_files/file_${i}.bin" bs=8097152 count=1
  done

  # Deploy all the files
  echo Deploying...
  assert_command dfx deploy -v

  # Verify that all files were uploaded by listing them
  assert_command dfx canister call e2e_project_frontend list '(record {})'
  for i in $(seq 1 70); do
    assert_match "/large_files/file_${i}.bin"
  done

  # Verify a few files can be retrieved
  assert_command dfx canister call --query e2e_project_frontend get "(record{key=\"/large_files/file_1.bin\";accept_encodings=vec{\"identity\"}})"
  assert_match 'total_length = 8_097_152'
  
  assert_command dfx canister call --query e2e_project_frontend get "(record{key=\"/large_files/file_35.bin\";accept_encodings=vec{\"identity\"}})"
  assert_match 'total_length = 8_097_152'
  
  assert_command dfx canister call --query e2e_project_frontend get "(record{key=\"/large_files/file_70.bin\";accept_encodings=vec{\"identity\"}})"
  assert_match 'total_length = 8_097_152'
}

Checklist:

• The title of this PR complies with Conventional Commits.
• I have edited the CHANGELOG accordingly.
• I have made corresponding changes to the documentation.