change pretty-calldata labels from decimal ints to hex values

[DJViau]

This PR changes the labels on pretty-calldata from decimal integers to hex labels, like one finds in the debugger.

For example,

 [0]:  0000000000000000000000000000000000000000000000000000000000000020
 [1]:  0000000000000000000000000000000000000000000000000000000000000002
 [2]:  0000000000000000000000000000000000000000000000000000000000000040
 [3]:  0000000000000000000000000000000000000000000000000000000000000140
 [4]:  000000000000000000000000da5a5adc64c8013d334a0da9e711b364af7a4c2d
 [5]:  0000000000000000000000000000000000000000000000000000000000000000
 [6]:  0000000000000000000000000000000000000000000000000000000000000000
 [7]:  0000000000000000000000000000000000000000000000000000000000000080
 [8]:  0000000000000000000000000000000000000000000000000000000000000044
 [9]:  40c10f19000000000000000000000000e05fcc23807536bee418f142d19fa0d2
 [10]: 1bb0cff700000000000000000000000000000000000000000000000000000000
 ...

becomes

 [000]: 0000000000000000000000000000000000000000000000000000000000000020
 [020]: 0000000000000000000000000000000000000000000000000000000000000002
 [040]: 0000000000000000000000000000000000000000000000000000000000000040
 [060]: 0000000000000000000000000000000000000000000000000000000000000140
 [080]: 000000000000000000000000da5a5adc64c8013d334a0da9e711b364af7a4c2d
 [0a0]: 0000000000000000000000000000000000000000000000000000000000000000
 [0c0]: 0000000000000000000000000000000000000000000000000000000000000000
 [0e0]: 0000000000000000000000000000000000000000000000000000000000000080
 [100]: 0000000000000000000000000000000000000000000000000000000000000044
 [120]: 40c10f19000000000000000000000000e05fcc23807536bee418f142d19fa0d2
 [140]: 1bb0cff700000000000000000000000000000000000000000000000000000000
 ...

Motivation

The integer labels require mental energy to convert to hex, which is how my team typically thinks of these. Converting to hex saves time and mental energy.

Solution

I updated the display method for PossibleSigs.

NOTE: This is my first time writing rust and my first time making this type of contribution. I read the contribution guidelines and attempted to follow their instructions, but I found some of the cargo checks hard to parse. I skipped opening an issue since the change is tiny and cosmetic. Please let me know what I need to do to properly comply with the letter and spirit of the contribution rules.

EDIT: This change also makes it easier to look up offsets.

[mattsse]

I don't have strong feelings about this.

wdyt @brockelmore ?

[emo-eth]

imo much easier for parsing out calldata offsets in calls with structs or dynamic parameters

[DJViau]

re: the label @mattsse assigned: this changes the behavior of cast pretty-calldata so that it behaves the same way the debugger does, so this should probably get the C-cast label in addition or instead.

[mattsse]

sgtm