Format contract id in fn_call event topic

[sisuresh]

What

Resolves #1463

Before

Event log (newest first):
0: [Diagnostic Event] contract:CAXDPD4A5ANAASQ2U74RBW7ULGB3TS5SGSAFYPN6O2R2IJKGEX22SWUS, topics:[error, Error(Contract, https://github.com/stellar/rs-soroban-env/pull/8)], data:["negative amount is not allowed", -1]
1: [Diagnostic Event] topics:[fn_call, Bytes(2e378f80e81a004a1aa7f910dbf45983b9cbb234805c3dbe76a3a4254625f5a9), mint], data:[GD4YHMIZ7IGW7E4XJ4TXIJPLJU255JXPM2PKTV6H4PA4N5RTM6T2R73D, -1]
2: [Diagnostic Event] contract:CAXDPD4A5ANAASQ2U74RBW7ULGB3TS5SGSAFYPN6O2R2IJKGEX22SWUS, topics:[fn_return, init_asset], data:Void
3: [Diagnostic Event] topics:[fn_call, Bytes(2e378f80e81a004a1aa7f910dbf45983b9cbb234805c3dbe76a3a4254625f5a9), init_asset], data:Bytes(00000001616161610000000000fc065517dbbca3e37ec0e97dbfcd80e6bcdfdac732be1e4152b259f1f7ea88)

After

Event log (newest first):
0: [Diagnostic Event] contract:CAXDPD4A5ANAASQ2U74RBW7ULGB3TS5SGSAFYPN6O2R2IJKGEX22SWUS, topics:[error, Error(Contract, https://github.com/stellar/rs-soroban-env/pull/8)], data:["negative amount is not allowed", -1]
1: [Diagnostic Event] topics:[fn_call, CAXDPD4A5ANAASQ2U74RBW7ULGB3TS5SGSAFYPN6O2R2IJKGEX22SWUS, mint], data:[GD4YHMIZ7IGW7E4XJ4TXIJPLJU255JXPM2PKTV6H4PA4N5RTM6T2R73D, -1]
2: [Diagnostic Event] contract:CAXDPD4A5ANAASQ2U74RBW7ULGB3TS5SGSAFYPN6O2R2IJKGEX22SWUS, topics:[fn_return, init_asset], data:Void
3: [Diagnostic Event] topics:[fn_call, CAXDPD4A5ANAASQ2U74RBW7ULGB3TS5SGSAFYPN6O2R2IJKGEX22SWUS, init_asset], data:Bytes(00000001616161610000000000fc065517dbbca3e37ec0e97dbfcd80e6bcdfdac732be1e4152b259f1f7ea88)