Add getNetworkRegisteredBlock view to SubnetPrecompile

[fine135]

Description

Adds getNetworkRegisteredBlock(uint16) as a view function to SubnetPrecompile, allowing smart contracts to query the block number at which a given subnet was registered. The function reads directly from NetworkRegisteredAt storage and explicitly records db_read_gas_cost so callers are correctly charged when invoked from within a contract.

Also adds the corresponding ABI entry to contract-tests/src/contracts/subnet.ts and an e2e test in contract-tests/test/precompileWrapper.direct-call.test.ts.

Related Issue(s)

• Relates 2455

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Other (please describe):

Breaking Change

N/A

Checklist

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have run ./scripts/fix_rust.sh to ensure my code is formatted and linted correctly
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

Screenshots (if applicable)

N/A

Additional Notes

The function follows the same pattern as other view functions in SubnetPrecompile (e.g. getServingRateLimit), with the addition of explicit gas metering via handle.record_cost(RuntimeHelper::<R>::db_read_gas_cost()) - unlike the existing view functions which omit this.