feat: adds functionality for Trials mode file parsing

[two4teezee]

This PR introduces localized changes to three files to support a universal Trials mode which will be delivered as a PR in the external modules repo (found here: ikemen-engine/modules#3). This parsing functionality is required to enable the most seamless Trials mode experience possible.

This PR modifies char.go to enable reading a trials.def file specified in the char's *.def file. Parsing of the trials data is done by this function and offers future growth functionality. Since the Trials mode is written in Lua, script.go is also modified to allow Lua functions to read the trials data parsed from the trials.def file. Finally, training.zss has a one line change to enable training functionality in Trials mode.

Details on the structure of trials.def files are included in the trials.lua PR (ikemen-engine/modules#3).

[two4teezee]

Resolved merge conflict... this is ready for review.

[two4teezee]

Updated description with links to Universal Trials Mode PR: ikemen-engine/modules#3. It's still in draft as I resolve some of the outstanding issues, but a compiled executable from this PR can be used to test the trials mode module.

[two4teezee]

Threw this back into draft. Adding some functionality as I do testing with more unique characters. Latest updates:

• Created functionality for checking variable-value pairs to determine whether a trial should be displayed. Useful for characters with grooves or special modes.
• Added the ability to pause checking for trial steps until the next hit. Useful when mode activation is desired as part of a combo, or at the start of a combo.

[two4teezee]

Added var-val pairs on a per-trial step basis to allow for checking var-val pairs during the trial step (separate from the trial display one var-val pairs).

[two4teezee]

This PR is no longer required. Trials mode is now a completely standalone Lua module.