test: increase exported functions limits for benchmarking setup

[maksymar]

This PR increases exported function limits for canister Wasm in benchmarking setup.

This allows canbench to have more tests, eg in stable-structures, at the same time it does not affect prod setup.

Current limitations for functions number and total function name length are 1k and 20k respectively.

For benchmarking purposes the number of functions increased x100 with the assumption that average function name length is 50 chars (previously was just 20).

[michael-weigelt]

Typically, we try to make most failure conditions that can occur on mainnet also occur with PocketIC, so that the user does not have green tests and then fails in prod.

However, in this case, the failure (that we let slide on PocketIC with this change) would occur very early on, when trying to upload a Wasm with too many exported methods. So I am fine with making this change without going through a PocketIC builder flag (which is the usual way to configure stuff that deviates from mainnet).

[mraszyk]

without going through a PocketIC builder flag

in a sense, this feature is already gated by using SubnetInstructionConfig::Benchmarking instead of SubnetInstructionConfig::Production although the name "instruction" config does not really apply anymore

[maksymar]

SubnetInstructionConfig::Benchmarking

I was also relying on this config, hope it's fine for this case.