Make `datadog-ci` suitable for parallel executions (esp. under Windows)

[rdesgroppes]

datadog-agent turns out to run several datadog-ci junit upload commands in parallel, which sometimes leads to spurious errors, like:

1. Error: EPERM: operation not permitted, lstat '\\?\C:\Users\ContainerAdministrator\AppData\Local\Temp\pkg-QunqPu\f6db2f7790c415a4726371e606fb3a9b4677c1226d9dfb63fd4798b687ee1579' (example)
2. Internal Error: warning: unable to access 'C:/Users/ContainerAdministrator/.gitconfig': Permission denied (example)

In order to address these limitations, could we:

1. use a dedicated temporary directory per process so as to avoid conflicting deletions at process termination time?
2. avoid mutating $HOME/.gitconfig unless strictly necessary? For instance here:

   • datadog-ci/src/commands/git-metadata/git.ts

     Line 24 in 5f5892d

     await git.addConfig('safe.directory', currentDir, true, GitConfigScope.global)

Meanwhile, following workarounds had to be put in place: (and backported to earlier release branches)

1. Alleviate temporary file conflicts in JUnit uploads datadog-agent#39544
2. Extend JUnit upload isolation to $HOME/.gitconfig datadog-agent#39524

Further references:

• JIRA ticket: ACIX-968
• Slack thread (until it expires): https://dd.slack.com/archives/C06PBHLD4DQ/p1754040098218369