Catch HTIF exceptions and fix TracerV bridge for larger iaddr widths

[abejgonzalez]

This PR does 2 things:

• Throw exceptions from program loading. Originally, if the HTIF thread threw an exception in VCS it would give a gibberish exception message to STDOUT. This PR instead catches that exception, prints something reasonable out to the console, and then errors.
• Fixes TracerV bridge for any iaddr width < 64. With the bump to SV48 in Chipyard, TracerV was broken since it expected the iaddr width to be 40 (and the valid bit to be in the 41th bit position). This fixes that assumption by just putting the valid bit at the end of integer (i.e. 64th bit).

Related PRs / Issues

UI / API Impact

Verilog / AGFI Compatibility

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[joonho3020]

LGTM